sched: Clean up scheduler_ipi()

[linux-2.6-microblaze.git] / kernel / sched / core.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  kernel/sched/core.c
 *
 *  Core kernel scheduler code and related syscalls
 *
 *  Copyright (C) 1991-2002  Linus Torvalds
 */
#include "sched.h"

#include <linux/nospec.h>

#include <linux/kcov.h>

#include <asm/switch_to.h>
#include <asm/tlb.h>

#include "../workqueue_internal.h"
#include "../../fs/io-wq.h"
#include "../smpboot.h"

#include "pelt.h"

#define CREATE_TRACE_POINTS
#include <trace/events/sched.h>

/*
 * Export tracepoints that act as a bare tracehook (ie: have no trace event
 * associated with them) to allow external modules to probe them.
 */
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_cfs_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_rt_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_dl_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_irq_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(pelt_se_tp);
EXPORT_TRACEPOINT_SYMBOL_GPL(sched_overutilized_tp);

DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);

#if defined(CONFIG_SCHED_DEBUG) && defined(CONFIG_JUMP_LABEL)
/*
 * Debugging: various feature bits
 *
 * If SCHED_DEBUG is disabled, each compilation unit has its own copy of
 * sysctl_sched_features, defined in sched.h, to allow constants propagation
 * at compile time and compiler optimization based on features default.
 */
#define SCHED_FEAT(name, enabled)       \
        (1UL << __SCHED_FEAT_##name) * enabled |
const_debug unsigned int sysctl_sched_features =
#include "features.h"
        0;
#undef SCHED_FEAT
#endif

/*
 * Number of tasks to iterate in a single balance run.
 * Limited because this is done with IRQs disabled.
 */
const_debug unsigned int sysctl_sched_nr_migrate = 32;

/*
 * period over which we measure -rt task CPU usage in us.
 * default: 1s
 */
unsigned int sysctl_sched_rt_period = 1000000;

__read_mostly int scheduler_running;

/*
 * part of the period that we allow rt tasks to run in us.
 * default: 0.95s
 */
int sysctl_sched_rt_runtime = 950000;

/*
 * __task_rq_lock - lock the rq @p resides on.
 */
struct rq *__task_rq_lock(struct task_struct *p, struct rq_flags *rf)
        __acquires(rq->lock)
{
        struct rq *rq;

        lockdep_assert_held(&p->pi_lock);

        for (;;) {
                rq = task_rq(p);
                raw_spin_lock(&rq->lock);
                if (likely(rq == task_rq(p) && !task_on_rq_migrating(p))) {
                        rq_pin_lock(rq, rf);
                        return rq;
                }
                raw_spin_unlock(&rq->lock);

                while (unlikely(task_on_rq_migrating(p)))
                        cpu_relax();
        }
}

/*
 * task_rq_lock - lock p->pi_lock and lock the rq @p resides on.
 */
struct rq *task_rq_lock(struct task_struct *p, struct rq_flags *rf)
        __acquires(p->pi_lock)
        __acquires(rq->lock)
{
        struct rq *rq;

        for (;;) {
                raw_spin_lock_irqsave(&p->pi_lock, rf->flags);
                rq = task_rq(p);
                raw_spin_lock(&rq->lock);
                /*
                 *      move_queued_task()              task_rq_lock()
                 *
                 *      ACQUIRE (rq->lock)
                 *      [S] ->on_rq = MIGRATING         [L] rq = task_rq()
                 *      WMB (__set_task_cpu())          ACQUIRE (rq->lock);
                 *      [S] ->cpu = new_cpu             [L] task_rq()
                 *                                      [L] ->on_rq
                 *      RELEASE (rq->lock)
                 *
                 * If we observe the old CPU in task_rq_lock(), the acquire of
                 * the old rq->lock will fully serialize against the stores.
                 *
                 * If we observe the new CPU in task_rq_lock(), the address
                 * dependency headed by '[L] rq = task_rq()' and the acquire
                 * will pair with the WMB to ensure we then also see migrating.
                 */
                if (likely(rq == task_rq(p) && !task_on_rq_migrating(p))) {
                        rq_pin_lock(rq, rf);
                        return rq;
                }
                raw_spin_unlock(&rq->lock);
                raw_spin_unlock_irqrestore(&p->pi_lock, rf->flags);

                while (unlikely(task_on_rq_migrating(p)))
                        cpu_relax();
        }
}

/*
 * RQ-clock updating methods:
 */

static void update_rq_clock_task(struct rq *rq, s64 delta)
{
/*
 * In theory, the compile should just see 0 here, and optimize out the call
 * to sched_rt_avg_update. But I don't trust it...
 */
        s64 __maybe_unused steal = 0, irq_delta = 0;

#ifdef CONFIG_IRQ_TIME_ACCOUNTING
        irq_delta = irq_time_read(cpu_of(rq)) - rq->prev_irq_time;

        /*
         * Since irq_time is only updated on {soft,}irq_exit, we might run into
         * this case when a previous update_rq_clock() happened inside a
         * {soft,}irq region.
         *
         * When this happens, we stop ->clock_task and only update the
         * prev_irq_time stamp to account for the part that fit, so that a next
         * update will consume the rest. This ensures ->clock_task is
         * monotonic.
         *
         * It does however cause some slight miss-attribution of {soft,}irq
         * time, a more accurate solution would be to update the irq_time using
         * the current rq->clock timestamp, except that would require using
         * atomic ops.
         */
        if (irq_delta > delta)
                irq_delta = delta;

        rq->prev_irq_time += irq_delta;
        delta -= irq_delta;
#endif
#ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING
        if (static_key_false((&paravirt_steal_rq_enabled))) {
                steal = paravirt_steal_clock(cpu_of(rq));
                steal -= rq->prev_steal_time_rq;

                if (unlikely(steal > delta))
                        steal = delta;

                rq->prev_steal_time_rq += steal;
                delta -= steal;
        }
#endif

        rq->clock_task += delta;

#ifdef CONFIG_HAVE_SCHED_AVG_IRQ
        if ((irq_delta + steal) && sched_feat(NONTASK_CAPACITY))
                update_irq_load_avg(rq, irq_delta + steal);
#endif
        update_rq_clock_pelt(rq, delta);
}

void update_rq_clock(struct rq *rq)
{
        s64 delta;

        lockdep_assert_held(&rq->lock);

        if (rq->clock_update_flags & RQCF_ACT_SKIP)
                return;

#ifdef CONFIG_SCHED_DEBUG
        if (sched_feat(WARN_DOUBLE_CLOCK))
                SCHED_WARN_ON(rq->clock_update_flags & RQCF_UPDATED);
        rq->clock_update_flags |= RQCF_UPDATED;
#endif

        delta = sched_clock_cpu(cpu_of(rq)) - rq->clock;
        if (delta < 0)
                return;
        rq->clock += delta;
        update_rq_clock_task(rq, delta);
}

static inline void
rq_csd_init(struct rq *rq, call_single_data_t *csd, smp_call_func_t func)
{
        csd->flags = 0;
        csd->func = func;
        csd->info = rq;
}

#ifdef CONFIG_SCHED_HRTICK
/*
 * Use HR-timers to deliver accurate preemption points.
 */

static void hrtick_clear(struct rq *rq)
{
        if (hrtimer_active(&rq->hrtick_timer))
                hrtimer_cancel(&rq->hrtick_timer);
}

/*
 * High-resolution timer tick.
 * Runs from hardirq context with interrupts disabled.
 */
static enum hrtimer_restart hrtick(struct hrtimer *timer)
{
        struct rq *rq = container_of(timer, struct rq, hrtick_timer);
        struct rq_flags rf;

        WARN_ON_ONCE(cpu_of(rq) != smp_processor_id());

        rq_lock(rq, &rf);
        update_rq_clock(rq);
        rq->curr->sched_class->task_tick(rq, rq->curr, 1);
        rq_unlock(rq, &rf);

        return HRTIMER_NORESTART;
}

#ifdef CONFIG_SMP

static void __hrtick_restart(struct rq *rq)
{
        struct hrtimer *timer = &rq->hrtick_timer;

        hrtimer_start_expires(timer, HRTIMER_MODE_ABS_PINNED_HARD);
}

/*
 * called from hardirq (IPI) context
 */
static void __hrtick_start(void *arg)
{
        struct rq *rq = arg;
        struct rq_flags rf;

        rq_lock(rq, &rf);
        __hrtick_restart(rq);
        rq_unlock(rq, &rf);
}

/*
 * Called to set the hrtick timer state.
 *
 * called with rq->lock held and irqs disabled
 */
void hrtick_start(struct rq *rq, u64 delay)
{
        struct hrtimer *timer = &rq->hrtick_timer;
        ktime_t time;
        s64 delta;

        /*
         * Don't schedule slices shorter than 10000ns, that just
         * doesn't make sense and can cause timer DoS.
         */
        delta = max_t(s64, delay, 10000LL);
        time = ktime_add_ns(timer->base->get_time(), delta);

        hrtimer_set_expires(timer, time);

        if (rq == this_rq())
                __hrtick_restart(rq);
        else
                smp_call_function_single_async(cpu_of(rq), &rq->hrtick_csd);
}

#else
/*
 * Called to set the hrtick timer state.
 *
 * called with rq->lock held and irqs disabled
 */
void hrtick_start(struct rq *rq, u64 delay)
{
        /*
         * Don't schedule slices shorter than 10000ns, that just
         * doesn't make sense. Rely on vruntime for fairness.
         */
        delay = max_t(u64, delay, 10000LL);
        hrtimer_start(&rq->hrtick_timer, ns_to_ktime(delay),
                      HRTIMER_MODE_REL_PINNED_HARD);
}

#endif /* CONFIG_SMP */

static void hrtick_rq_init(struct rq *rq)
{
#ifdef CONFIG_SMP
        rq_csd_init(rq, &rq->hrtick_csd, __hrtick_start);
#endif
        hrtimer_init(&rq->hrtick_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
        rq->hrtick_timer.function = hrtick;
}
#else   /* CONFIG_SCHED_HRTICK */
static inline void hrtick_clear(struct rq *rq)
{
}

static inline void hrtick_rq_init(struct rq *rq)
{
}
#endif  /* CONFIG_SCHED_HRTICK */

/*
 * cmpxchg based fetch_or, macro so it works for different integer types
 */
#define fetch_or(ptr, mask)                                             \
        ({                                                              \
                typeof(ptr) _ptr = (ptr);                               \
                typeof(mask) _mask = (mask);                            \
                typeof(*_ptr) _old, _val = *_ptr;                       \
                                                                        \
                for (;;) {                                              \
                        _old = cmpxchg(_ptr, _val, _val | _mask);       \
                        if (_old == _val)                               \
                                break;                                  \
                        _val = _old;                                    \
                }                                                       \
        _old;                                                           \
})

#if defined(CONFIG_SMP) && defined(TIF_POLLING_NRFLAG)
/*
 * Atomically set TIF_NEED_RESCHED and test for TIF_POLLING_NRFLAG,
 * this avoids any races wrt polling state changes and thereby avoids
 * spurious IPIs.
 */
static bool set_nr_and_not_polling(struct task_struct *p)
{
        struct thread_info *ti = task_thread_info(p);
        return !(fetch_or(&ti->flags, _TIF_NEED_RESCHED) & _TIF_POLLING_NRFLAG);
}

/*
 * Atomically set TIF_NEED_RESCHED if TIF_POLLING_NRFLAG is set.
 *
 * If this returns true, then the idle task promises to call
 * sched_ttwu_pending() and reschedule soon.
 */
static bool set_nr_if_polling(struct task_struct *p)
{
        struct thread_info *ti = task_thread_info(p);
        typeof(ti->flags) old, val = READ_ONCE(ti->flags);

        for (;;) {
                if (!(val & _TIF_POLLING_NRFLAG))
                        return false;
                if (val & _TIF_NEED_RESCHED)
                        return true;
                old = cmpxchg(&ti->flags, val, val | _TIF_NEED_RESCHED);
                if (old == val)
                        break;
                val = old;
        }
        return true;
}

#else
static bool set_nr_and_not_polling(struct task_struct *p)
{
        set_tsk_need_resched(p);
        return true;
}

#ifdef CONFIG_SMP
static bool set_nr_if_polling(struct task_struct *p)
{
        return false;
}
#endif
#endif

static bool __wake_q_add(struct wake_q_head *head, struct task_struct *task)
{
        struct wake_q_node *node = &task->wake_q;

        /*
         * Atomically grab the task, if ->wake_q is !nil already it means
         * its already queued (either by us or someone else) and will get the
         * wakeup due to that.
         *
         * In order to ensure that a pending wakeup will observe our pending
         * state, even in the failed case, an explicit smp_mb() must be used.
         */
        smp_mb__before_atomic();
        if (unlikely(cmpxchg_relaxed(&node->next, NULL, WAKE_Q_TAIL)))
                return false;

        /*
         * The head is context local, there can be no concurrency.
         */
        *head->lastp = node;
        head->lastp = &node->next;
        return true;
}

/**
 * wake_q_add() - queue a wakeup for 'later' waking.
 * @head: the wake_q_head to add @task to
 * @task: the task to queue for 'later' wakeup
 *
 * Queue a task for later wakeup, most likely by the wake_up_q() call in the
 * same context, _HOWEVER_ this is not guaranteed, the wakeup can come
 * instantly.
 *
 * This function must be used as-if it were wake_up_process(); IOW the task
 * must be ready to be woken at this location.
 */
void wake_q_add(struct wake_q_head *head, struct task_struct *task)
{
        if (__wake_q_add(head, task))
                get_task_struct(task);
}

/**
 * wake_q_add_safe() - safely queue a wakeup for 'later' waking.
 * @head: the wake_q_head to add @task to
 * @task: the task to queue for 'later' wakeup
 *
 * Queue a task for later wakeup, most likely by the wake_up_q() call in the
 * same context, _HOWEVER_ this is not guaranteed, the wakeup can come
 * instantly.
 *
 * This function must be used as-if it were wake_up_process(); IOW the task
 * must be ready to be woken at this location.
 *
 * This function is essentially a task-safe equivalent to wake_q_add(). Callers
 * that already hold reference to @task can call the 'safe' version and trust
 * wake_q to do the right thing depending whether or not the @task is already
 * queued for wakeup.
 */
void wake_q_add_safe(struct wake_q_head *head, struct task_struct *task)
{
        if (!__wake_q_add(head, task))
                put_task_struct(task);
}

void wake_up_q(struct wake_q_head *head)
{
        struct wake_q_node *node = head->first;

        while (node != WAKE_Q_TAIL) {
                struct task_struct *task;

                task = container_of(node, struct task_struct, wake_q);
                BUG_ON(!task);
                /* Task can safely be re-inserted now: */
                node = node->next;
                task->wake_q.next = NULL;

                /*
                 * wake_up_process() executes a full barrier, which pairs with
                 * the queueing in wake_q_add() so as not to miss wakeups.
                 */
                wake_up_process(task);
                put_task_struct(task);
        }
}

/*
 * resched_curr - mark rq's current task 'to be rescheduled now'.
 *
 * On UP this means the setting of the need_resched flag, on SMP it
 * might also involve a cross-CPU call to trigger the scheduler on
 * the target CPU.
 */
void resched_curr(struct rq *rq)
{
        struct task_struct *curr = rq->curr;
        int cpu;

        lockdep_assert_held(&rq->lock);

        if (test_tsk_need_resched(curr))
                return;

        cpu = cpu_of(rq);

        if (cpu == smp_processor_id()) {
                set_tsk_need_resched(curr);
                set_preempt_need_resched();
                return;
        }

        if (set_nr_and_not_polling(curr))
                smp_send_reschedule(cpu);
        else
                trace_sched_wake_idle_without_ipi(cpu);
}

void resched_cpu(int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        unsigned long flags;

        raw_spin_lock_irqsave(&rq->lock, flags);
        if (cpu_online(cpu) || cpu == smp_processor_id())
                resched_curr(rq);
        raw_spin_unlock_irqrestore(&rq->lock, flags);
}

#ifdef CONFIG_SMP
#ifdef CONFIG_NO_HZ_COMMON
/*
 * In the semi idle case, use the nearest busy CPU for migrating timers
 * from an idle CPU.  This is good for power-savings.
 *
 * We don't do similar optimization for completely idle system, as
 * selecting an idle CPU will add more delays to the timers than intended
 * (as that CPU's timer base may not be uptodate wrt jiffies etc).
 */
int get_nohz_timer_target(void)
{
        int i, cpu = smp_processor_id(), default_cpu = -1;
        struct sched_domain *sd;

        if (housekeeping_cpu(cpu, HK_FLAG_TIMER)) {
                if (!idle_cpu(cpu))
                        return cpu;
                default_cpu = cpu;
        }

        rcu_read_lock();
        for_each_domain(cpu, sd) {
                for_each_cpu_and(i, sched_domain_span(sd),
                        housekeeping_cpumask(HK_FLAG_TIMER)) {
                        if (cpu == i)
                                continue;

                        if (!idle_cpu(i)) {
                                cpu = i;
                                goto unlock;
                        }
                }
        }

        if (default_cpu == -1)
                default_cpu = housekeeping_any_cpu(HK_FLAG_TIMER);
        cpu = default_cpu;
unlock:
        rcu_read_unlock();
        return cpu;
}

/*
 * When add_timer_on() enqueues a timer into the timer wheel of an
 * idle CPU then this timer might expire before the next timer event
 * which is scheduled to wake up that CPU. In case of a completely
 * idle system the next event might even be infinite time into the
 * future. wake_up_idle_cpu() ensures that the CPU is woken up and
 * leaves the inner idle loop so the newly added timer is taken into
 * account when the CPU goes back to idle and evaluates the timer
 * wheel for the next timer event.
 */
static void wake_up_idle_cpu(int cpu)
{
        struct rq *rq = cpu_rq(cpu);

        if (cpu == smp_processor_id())
                return;

        if (set_nr_and_not_polling(rq->idle))
                smp_send_reschedule(cpu);
        else
                trace_sched_wake_idle_without_ipi(cpu);
}

static bool wake_up_full_nohz_cpu(int cpu)
{
        /*
         * We just need the target to call irq_exit() and re-evaluate
         * the next tick. The nohz full kick at least implies that.
         * If needed we can still optimize that later with an
         * empty IRQ.
         */
        if (cpu_is_offline(cpu))
                return true;  /* Don't try to wake offline CPUs. */
        if (tick_nohz_full_cpu(cpu)) {
                if (cpu != smp_processor_id() ||
                    tick_nohz_tick_stopped())
                        tick_nohz_full_kick_cpu(cpu);
                return true;
        }

        return false;
}

/*
 * Wake up the specified CPU.  If the CPU is going offline, it is the
 * caller's responsibility to deal with the lost wakeup, for example,
 * by hooking into the CPU_DEAD notifier like timers and hrtimers do.
 */
void wake_up_nohz_cpu(int cpu)
{
        if (!wake_up_full_nohz_cpu(cpu))
                wake_up_idle_cpu(cpu);
}

static inline bool got_nohz_idle_kick(void)
{
        int cpu = smp_processor_id();

        if (!(atomic_read(nohz_flags(cpu)) & NOHZ_KICK_MASK))
                return false;

        if (idle_cpu(cpu) && !need_resched())
                return true;

        /*
         * We can't run Idle Load Balance on this CPU for this time so we
         * cancel it and clear NOHZ_BALANCE_KICK
         */
        atomic_andnot(NOHZ_KICK_MASK, nohz_flags(cpu));
        return false;
}

static void nohz_csd_func(void *info)
{
        struct rq *rq = info;

        if (got_nohz_idle_kick()) {
                rq->idle_balance = 1;
                raise_softirq_irqoff(SCHED_SOFTIRQ);
        }
}

#else /* CONFIG_NO_HZ_COMMON */

static inline bool got_nohz_idle_kick(void)
{
        return false;
}

#endif /* CONFIG_NO_HZ_COMMON */

#ifdef CONFIG_NO_HZ_FULL
bool sched_can_stop_tick(struct rq *rq)
{
        int fifo_nr_running;

        /* Deadline tasks, even if single, need the tick */
        if (rq->dl.dl_nr_running)
                return false;

        /*
         * If there are more than one RR tasks, we need the tick to effect the
         * actual RR behaviour.
         */
        if (rq->rt.rr_nr_running) {
                if (rq->rt.rr_nr_running == 1)
                        return true;
                else
                        return false;
        }

        /*
         * If there's no RR tasks, but FIFO tasks, we can skip the tick, no
         * forced preemption between FIFO tasks.
         */
        fifo_nr_running = rq->rt.rt_nr_running - rq->rt.rr_nr_running;
        if (fifo_nr_running)
                return true;

        /*
         * If there are no DL,RR/FIFO tasks, there must only be CFS tasks left;
         * if there's more than one we need the tick for involuntary
         * preemption.
         */
        if (rq->nr_running > 1)
                return false;

        return true;
}
#endif /* CONFIG_NO_HZ_FULL */
#endif /* CONFIG_SMP */

#if defined(CONFIG_RT_GROUP_SCHED) || (defined(CONFIG_FAIR_GROUP_SCHED) && \
                        (defined(CONFIG_SMP) || defined(CONFIG_CFS_BANDWIDTH)))
/*
 * Iterate task_group tree rooted at *from, calling @down when first entering a
 * node and @up when leaving it for the final time.
 *
 * Caller must hold rcu_lock or sufficient equivalent.
 */
int walk_tg_tree_from(struct task_group *from,
                             tg_visitor down, tg_visitor up, void *data)
{
        struct task_group *parent, *child;
        int ret;

        parent = from;

down:
        ret = (*down)(parent, data);
        if (ret)
                goto out;
        list_for_each_entry_rcu(child, &parent->children, siblings) {
                parent = child;
                goto down;

up:
                continue;
        }
        ret = (*up)(parent, data);
        if (ret || parent == from)
                goto out;

        child = parent;
        parent = parent->parent;
        if (parent)
                goto up;
out:
        return ret;
}

int tg_nop(struct task_group *tg, void *data)
{
        return 0;
}
#endif

static void set_load_weight(struct task_struct *p, bool update_load)
{
        int prio = p->static_prio - MAX_RT_PRIO;
        struct load_weight *load = &p->se.load;

        /*
         * SCHED_IDLE tasks get minimal weight:
         */
        if (task_has_idle_policy(p)) {
                load->weight = scale_load(WEIGHT_IDLEPRIO);
                load->inv_weight = WMULT_IDLEPRIO;
                return;
        }

        /*
         * SCHED_OTHER tasks have to update their load when changing their
         * weight
         */
        if (update_load && p->sched_class == &fair_sched_class) {
                reweight_task(p, prio);
        } else {
                load->weight = scale_load(sched_prio_to_weight[prio]);
                load->inv_weight = sched_prio_to_wmult[prio];
        }
}

#ifdef CONFIG_UCLAMP_TASK
/*
 * Serializes updates of utilization clamp values
 *
 * The (slow-path) user-space triggers utilization clamp value updates which
 * can require updates on (fast-path) scheduler's data structures used to
 * support enqueue/dequeue operations.
 * While the per-CPU rq lock protects fast-path update operations, user-space
 * requests are serialized using a mutex to reduce the risk of conflicting
 * updates or API abuses.
 */
static DEFINE_MUTEX(uclamp_mutex);

/* Max allowed minimum utilization */
unsigned int sysctl_sched_uclamp_util_min = SCHED_CAPACITY_SCALE;

/* Max allowed maximum utilization */
unsigned int sysctl_sched_uclamp_util_max = SCHED_CAPACITY_SCALE;

/* All clamps are required to be less or equal than these values */
static struct uclamp_se uclamp_default[UCLAMP_CNT];

/* Integer rounded range for each bucket */
#define UCLAMP_BUCKET_DELTA DIV_ROUND_CLOSEST(SCHED_CAPACITY_SCALE, UCLAMP_BUCKETS)

#define for_each_clamp_id(clamp_id) \
        for ((clamp_id) = 0; (clamp_id) < UCLAMP_CNT; (clamp_id)++)

static inline unsigned int uclamp_bucket_id(unsigned int clamp_value)
{
        return clamp_value / UCLAMP_BUCKET_DELTA;
}

static inline unsigned int uclamp_bucket_base_value(unsigned int clamp_value)
{
        return UCLAMP_BUCKET_DELTA * uclamp_bucket_id(clamp_value);
}

static inline unsigned int uclamp_none(enum uclamp_id clamp_id)
{
        if (clamp_id == UCLAMP_MIN)
                return 0;
        return SCHED_CAPACITY_SCALE;
}

static inline void uclamp_se_set(struct uclamp_se *uc_se,
                                 unsigned int value, bool user_defined)
{
        uc_se->value = value;
        uc_se->bucket_id = uclamp_bucket_id(value);
        uc_se->user_defined = user_defined;
}

static inline unsigned int
uclamp_idle_value(struct rq *rq, enum uclamp_id clamp_id,
                  unsigned int clamp_value)
{
        /*
         * Avoid blocked utilization pushing up the frequency when we go
         * idle (which drops the max-clamp) by retaining the last known
         * max-clamp.
         */
        if (clamp_id == UCLAMP_MAX) {
                rq->uclamp_flags |= UCLAMP_FLAG_IDLE;
                return clamp_value;
        }

        return uclamp_none(UCLAMP_MIN);
}

static inline void uclamp_idle_reset(struct rq *rq, enum uclamp_id clamp_id,
                                     unsigned int clamp_value)
{
        /* Reset max-clamp retention only on idle exit */
        if (!(rq->uclamp_flags & UCLAMP_FLAG_IDLE))
                return;

        WRITE_ONCE(rq->uclamp[clamp_id].value, clamp_value);
}

static inline
unsigned int uclamp_rq_max_value(struct rq *rq, enum uclamp_id clamp_id,
                                   unsigned int clamp_value)
{
        struct uclamp_bucket *bucket = rq->uclamp[clamp_id].bucket;
        int bucket_id = UCLAMP_BUCKETS - 1;

        /*
         * Since both min and max clamps are max aggregated, find the
         * top most bucket with tasks in.
         */
        for ( ; bucket_id >= 0; bucket_id--) {
                if (!bucket[bucket_id].tasks)
                        continue;
                return bucket[bucket_id].value;
        }

        /* No tasks -- default clamp values */
        return uclamp_idle_value(rq, clamp_id, clamp_value);
}

static inline struct uclamp_se
uclamp_tg_restrict(struct task_struct *p, enum uclamp_id clamp_id)
{
        struct uclamp_se uc_req = p->uclamp_req[clamp_id];
#ifdef CONFIG_UCLAMP_TASK_GROUP
        struct uclamp_se uc_max;

        /*
         * Tasks in autogroups or root task group will be
         * restricted by system defaults.
         */
        if (task_group_is_autogroup(task_group(p)))
                return uc_req;
        if (task_group(p) == &root_task_group)
                return uc_req;

        uc_max = task_group(p)->uclamp[clamp_id];
        if (uc_req.value > uc_max.value || !uc_req.user_defined)
                return uc_max;
#endif

        return uc_req;
}

/*
 * The effective clamp bucket index of a task depends on, by increasing
 * priority:
 * - the task specific clamp value, when explicitly requested from userspace
 * - the task group effective clamp value, for tasks not either in the root
 *   group or in an autogroup
 * - the system default clamp value, defined by the sysadmin
 */
static inline struct uclamp_se
uclamp_eff_get(struct task_struct *p, enum uclamp_id clamp_id)
{
        struct uclamp_se uc_req = uclamp_tg_restrict(p, clamp_id);
        struct uclamp_se uc_max = uclamp_default[clamp_id];

        /* System default restrictions always apply */
        if (unlikely(uc_req.value > uc_max.value))
                return uc_max;

        return uc_req;
}

unsigned long uclamp_eff_value(struct task_struct *p, enum uclamp_id clamp_id)
{
        struct uclamp_se uc_eff;

        /* Task currently refcounted: use back-annotated (effective) value */
        if (p->uclamp[clamp_id].active)
                return (unsigned long)p->uclamp[clamp_id].value;

        uc_eff = uclamp_eff_get(p, clamp_id);

        return (unsigned long)uc_eff.value;
}

/*
 * When a task is enqueued on a rq, the clamp bucket currently defined by the
 * task's uclamp::bucket_id is refcounted on that rq. This also immediately
 * updates the rq's clamp value if required.
 *
 * Tasks can have a task-specific value requested from user-space, track
 * within each bucket the maximum value for tasks refcounted in it.
 * This "local max aggregation" allows to track the exact "requested" value
 * for each bucket when all its RUNNABLE tasks require the same clamp.
 */
static inline void uclamp_rq_inc_id(struct rq *rq, struct task_struct *p,
                                    enum uclamp_id clamp_id)
{
        struct uclamp_rq *uc_rq = &rq->uclamp[clamp_id];
        struct uclamp_se *uc_se = &p->uclamp[clamp_id];
        struct uclamp_bucket *bucket;

        lockdep_assert_held(&rq->lock);

        /* Update task effective clamp */
        p->uclamp[clamp_id] = uclamp_eff_get(p, clamp_id);

        bucket = &uc_rq->bucket[uc_se->bucket_id];
        bucket->tasks++;
        uc_se->active = true;

        uclamp_idle_reset(rq, clamp_id, uc_se->value);

        /*
         * Local max aggregation: rq buckets always track the max
         * "requested" clamp value of its RUNNABLE tasks.
         */
        if (bucket->tasks == 1 || uc_se->value > bucket->value)
                bucket->value = uc_se->value;

        if (uc_se->value > READ_ONCE(uc_rq->value))
                WRITE_ONCE(uc_rq->value, uc_se->value);
}

/*
 * When a task is dequeued from a rq, the clamp bucket refcounted by the task
 * is released. If this is the last task reference counting the rq's max
 * active clamp value, then the rq's clamp value is updated.
 *
 * Both refcounted tasks and rq's cached clamp values are expected to be
 * always valid. If it's detected they are not, as defensive programming,
 * enforce the expected state and warn.
 */
static inline void uclamp_rq_dec_id(struct rq *rq, struct task_struct *p,
                                    enum uclamp_id clamp_id)
{
        struct uclamp_rq *uc_rq = &rq->uclamp[clamp_id];
        struct uclamp_se *uc_se = &p->uclamp[clamp_id];
        struct uclamp_bucket *bucket;
        unsigned int bkt_clamp;
        unsigned int rq_clamp;

        lockdep_assert_held(&rq->lock);

        bucket = &uc_rq->bucket[uc_se->bucket_id];
        SCHED_WARN_ON(!bucket->tasks);
        if (likely(bucket->tasks))
                bucket->tasks--;
        uc_se->active = false;

        /*
         * Keep "local max aggregation" simple and accept to (possibly)
         * overboost some RUNNABLE tasks in the same bucket.
         * The rq clamp bucket value is reset to its base value whenever
         * there are no more RUNNABLE tasks refcounting it.
         */
        if (likely(bucket->tasks))
                return;

        rq_clamp = READ_ONCE(uc_rq->value);
        /*
         * Defensive programming: this should never happen. If it happens,
         * e.g. due to future modification, warn and fixup the expected value.
         */
        SCHED_WARN_ON(bucket->value > rq_clamp);
        if (bucket->value >= rq_clamp) {
                bkt_clamp = uclamp_rq_max_value(rq, clamp_id, uc_se->value);
                WRITE_ONCE(uc_rq->value, bkt_clamp);
        }
}

static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p)
{
        enum uclamp_id clamp_id;

        if (unlikely(!p->sched_class->uclamp_enabled))
                return;

        for_each_clamp_id(clamp_id)
                uclamp_rq_inc_id(rq, p, clamp_id);

        /* Reset clamp idle holding when there is one RUNNABLE task */
        if (rq->uclamp_flags & UCLAMP_FLAG_IDLE)
                rq->uclamp_flags &= ~UCLAMP_FLAG_IDLE;
}

static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p)
{
        enum uclamp_id clamp_id;

        if (unlikely(!p->sched_class->uclamp_enabled))
                return;

        for_each_clamp_id(clamp_id)
                uclamp_rq_dec_id(rq, p, clamp_id);
}

static inline void
uclamp_update_active(struct task_struct *p, enum uclamp_id clamp_id)
{
        struct rq_flags rf;
        struct rq *rq;

        /*
         * Lock the task and the rq where the task is (or was) queued.
         *
         * We might lock the (previous) rq of a !RUNNABLE task, but that's the
         * price to pay to safely serialize util_{min,max} updates with
         * enqueues, dequeues and migration operations.
         * This is the same locking schema used by __set_cpus_allowed_ptr().
         */
        rq = task_rq_lock(p, &rf);

        /*
         * Setting the clamp bucket is serialized by task_rq_lock().
         * If the task is not yet RUNNABLE and its task_struct is not
         * affecting a valid clamp bucket, the next time it's enqueued,
         * it will already see the updated clamp bucket value.
         */
        if (p->uclamp[clamp_id].active) {
                uclamp_rq_dec_id(rq, p, clamp_id);
                uclamp_rq_inc_id(rq, p, clamp_id);
        }

        task_rq_unlock(rq, p, &rf);
}

#ifdef CONFIG_UCLAMP_TASK_GROUP
static inline void
uclamp_update_active_tasks(struct cgroup_subsys_state *css,
                           unsigned int clamps)
{
        enum uclamp_id clamp_id;
        struct css_task_iter it;
        struct task_struct *p;

        css_task_iter_start(css, 0, &it);
        while ((p = css_task_iter_next(&it))) {
                for_each_clamp_id(clamp_id) {
                        if ((0x1 << clamp_id) & clamps)
                                uclamp_update_active(p, clamp_id);
                }
        }
        css_task_iter_end(&it);
}

static void cpu_util_update_eff(struct cgroup_subsys_state *css);
static void uclamp_update_root_tg(void)
{
        struct task_group *tg = &root_task_group;

        uclamp_se_set(&tg->uclamp_req[UCLAMP_MIN],
                      sysctl_sched_uclamp_util_min, false);
        uclamp_se_set(&tg->uclamp_req[UCLAMP_MAX],
                      sysctl_sched_uclamp_util_max, false);

        rcu_read_lock();
        cpu_util_update_eff(&root_task_group.css);
        rcu_read_unlock();
}
#else
static void uclamp_update_root_tg(void) { }
#endif

int sysctl_sched_uclamp_handler(struct ctl_table *table, int write,
                                void __user *buffer, size_t *lenp,
                                loff_t *ppos)
{
        bool update_root_tg = false;
        int old_min, old_max;
        int result;

        mutex_lock(&uclamp_mutex);
        old_min = sysctl_sched_uclamp_util_min;
        old_max = sysctl_sched_uclamp_util_max;

        result = proc_dointvec(table, write, buffer, lenp, ppos);
        if (result)
                goto undo;
        if (!write)
                goto done;

        if (sysctl_sched_uclamp_util_min > sysctl_sched_uclamp_util_max ||
            sysctl_sched_uclamp_util_max > SCHED_CAPACITY_SCALE) {
                result = -EINVAL;
                goto undo;
        }

        if (old_min != sysctl_sched_uclamp_util_min) {
                uclamp_se_set(&uclamp_default[UCLAMP_MIN],
                              sysctl_sched_uclamp_util_min, false);
                update_root_tg = true;
        }
        if (old_max != sysctl_sched_uclamp_util_max) {
                uclamp_se_set(&uclamp_default[UCLAMP_MAX],
                              sysctl_sched_uclamp_util_max, false);
                update_root_tg = true;
        }

        if (update_root_tg)
                uclamp_update_root_tg();

        /*
         * We update all RUNNABLE tasks only when task groups are in use.
         * Otherwise, keep it simple and do just a lazy update at each next
         * task enqueue time.
         */

        goto done;

undo:
        sysctl_sched_uclamp_util_min = old_min;
        sysctl_sched_uclamp_util_max = old_max;
done:
        mutex_unlock(&uclamp_mutex);

        return result;
}

static int uclamp_validate(struct task_struct *p,
                           const struct sched_attr *attr)
{
        unsigned int lower_bound = p->uclamp_req[UCLAMP_MIN].value;
        unsigned int upper_bound = p->uclamp_req[UCLAMP_MAX].value;

        if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN)
                lower_bound = attr->sched_util_min;
        if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX)
                upper_bound = attr->sched_util_max;

        if (lower_bound > upper_bound)
                return -EINVAL;
        if (upper_bound > SCHED_CAPACITY_SCALE)
                return -EINVAL;

        return 0;
}

static void __setscheduler_uclamp(struct task_struct *p,
                                  const struct sched_attr *attr)
{
        enum uclamp_id clamp_id;

        /*
         * On scheduling class change, reset to default clamps for tasks
         * without a task-specific value.
         */
        for_each_clamp_id(clamp_id) {
                struct uclamp_se *uc_se = &p->uclamp_req[clamp_id];
                unsigned int clamp_value = uclamp_none(clamp_id);

                /* Keep using defined clamps across class changes */
                if (uc_se->user_defined)
                        continue;

                /* By default, RT tasks always get 100% boost */
                if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN))
                        clamp_value = uclamp_none(UCLAMP_MAX);

                uclamp_se_set(uc_se, clamp_value, false);
        }

        if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)))
                return;

        if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) {
                uclamp_se_set(&p->uclamp_req[UCLAMP_MIN],
                              attr->sched_util_min, true);
        }

        if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MAX) {
                uclamp_se_set(&p->uclamp_req[UCLAMP_MAX],
                              attr->sched_util_max, true);
        }
}

static void uclamp_fork(struct task_struct *p)
{
        enum uclamp_id clamp_id;

        for_each_clamp_id(clamp_id)
                p->uclamp[clamp_id].active = false;

        if (likely(!p->sched_reset_on_fork))
                return;

        for_each_clamp_id(clamp_id) {
                uclamp_se_set(&p->uclamp_req[clamp_id],
                              uclamp_none(clamp_id), false);
        }
}

static void __init init_uclamp(void)
{
        struct uclamp_se uc_max = {};
        enum uclamp_id clamp_id;
        int cpu;

        mutex_init(&uclamp_mutex);

        for_each_possible_cpu(cpu) {
                memset(&cpu_rq(cpu)->uclamp, 0,
                                sizeof(struct uclamp_rq)*UCLAMP_CNT);
                cpu_rq(cpu)->uclamp_flags = 0;
        }

        for_each_clamp_id(clamp_id) {
                uclamp_se_set(&init_task.uclamp_req[clamp_id],
                              uclamp_none(clamp_id), false);
        }

        /* System defaults allow max clamp values for both indexes */
        uclamp_se_set(&uc_max, uclamp_none(UCLAMP_MAX), false);
        for_each_clamp_id(clamp_id) {
                uclamp_default[clamp_id] = uc_max;
#ifdef CONFIG_UCLAMP_TASK_GROUP
                root_task_group.uclamp_req[clamp_id] = uc_max;
                root_task_group.uclamp[clamp_id] = uc_max;
#endif
        }
}

#else /* CONFIG_UCLAMP_TASK */
static inline void uclamp_rq_inc(struct rq *rq, struct task_struct *p) { }
static inline void uclamp_rq_dec(struct rq *rq, struct task_struct *p) { }
static inline int uclamp_validate(struct task_struct *p,
                                  const struct sched_attr *attr)
{
        return -EOPNOTSUPP;
}
static void __setscheduler_uclamp(struct task_struct *p,
                                  const struct sched_attr *attr) { }
static inline void uclamp_fork(struct task_struct *p) { }
static inline void init_uclamp(void) { }
#endif /* CONFIG_UCLAMP_TASK */

static inline void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
{
        if (!(flags & ENQUEUE_NOCLOCK))
                update_rq_clock(rq);

        if (!(flags & ENQUEUE_RESTORE)) {
                sched_info_queued(rq, p);
                psi_enqueue(p, flags & ENQUEUE_WAKEUP);
        }

        uclamp_rq_inc(rq, p);
        p->sched_class->enqueue_task(rq, p, flags);
}

static inline void dequeue_task(struct rq *rq, struct task_struct *p, int flags)
{
        if (!(flags & DEQUEUE_NOCLOCK))
                update_rq_clock(rq);

        if (!(flags & DEQUEUE_SAVE)) {
                sched_info_dequeued(rq, p);
                psi_dequeue(p, flags & DEQUEUE_SLEEP);
        }

        uclamp_rq_dec(rq, p);
        p->sched_class->dequeue_task(rq, p, flags);
}

void activate_task(struct rq *rq, struct task_struct *p, int flags)
{
        if (task_contributes_to_load(p))
                rq->nr_uninterruptible--;

        enqueue_task(rq, p, flags);

        p->on_rq = TASK_ON_RQ_QUEUED;
}

void deactivate_task(struct rq *rq, struct task_struct *p, int flags)
{
        p->on_rq = (flags & DEQUEUE_SLEEP) ? 0 : TASK_ON_RQ_MIGRATING;

        if (task_contributes_to_load(p))
                rq->nr_uninterruptible++;

        dequeue_task(rq, p, flags);
}

/*
 * __normal_prio - return the priority that is based on the static prio
 */
static inline int __normal_prio(struct task_struct *p)
{
        return p->static_prio;
}

/*
 * Calculate the expected normal priority: i.e. priority
 * without taking RT-inheritance into account. Might be
 * boosted by interactivity modifiers. Changes upon fork,
 * setprio syscalls, and whenever the interactivity
 * estimator recalculates.
 */
static inline int normal_prio(struct task_struct *p)
{
        int prio;

        if (task_has_dl_policy(p))
                prio = MAX_DL_PRIO-1;
        else if (task_has_rt_policy(p))
                prio = MAX_RT_PRIO-1 - p->rt_priority;
        else
                prio = __normal_prio(p);
        return prio;
}

/*
 * Calculate the current priority, i.e. the priority
 * taken into account by the scheduler. This value might
 * be boosted by RT tasks, or might be boosted by
 * interactivity modifiers. Will be RT if the task got
 * RT-boosted. If not then it returns p->normal_prio.
 */
static int effective_prio(struct task_struct *p)
{
        p->normal_prio = normal_prio(p);
        /*
         * If we are RT tasks or we were boosted to RT priority,
         * keep the priority unchanged. Otherwise, update priority
         * to the normal priority:
         */
        if (!rt_prio(p->prio))
                return p->normal_prio;
        return p->prio;
}

/**
 * task_curr - is this task currently executing on a CPU?
 * @p: the task in question.
 *
 * Return: 1 if the task is currently executing. 0 otherwise.
 */
inline int task_curr(const struct task_struct *p)
{
        return cpu_curr(task_cpu(p)) == p;
}

/*
 * switched_from, switched_to and prio_changed must _NOT_ drop rq->lock,
 * use the balance_callback list if you want balancing.
 *
 * this means any call to check_class_changed() must be followed by a call to
 * balance_callback().
 */
static inline void check_class_changed(struct rq *rq, struct task_struct *p,
                                       const struct sched_class *prev_class,
                                       int oldprio)
{
        if (prev_class != p->sched_class) {
                if (prev_class->switched_from)
                        prev_class->switched_from(rq, p);

                p->sched_class->switched_to(rq, p);
        } else if (oldprio != p->prio || dl_task(p))
                p->sched_class->prio_changed(rq, p, oldprio);
}

void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)
{
        const struct sched_class *class;

        if (p->sched_class == rq->curr->sched_class) {
                rq->curr->sched_class->check_preempt_curr(rq, p, flags);
        } else {
                for_each_class(class) {
                        if (class == rq->curr->sched_class)
                                break;
                        if (class == p->sched_class) {
                                resched_curr(rq);
                                break;
                        }
                }
        }

        /*
         * A queue event has occurred, and we're going to schedule.  In
         * this case, we can save a useless back to back clock update.
         */
        if (task_on_rq_queued(rq->curr) && test_tsk_need_resched(rq->curr))
                rq_clock_skip_update(rq);
}

#ifdef CONFIG_SMP

/*
 * Per-CPU kthreads are allowed to run on !active && online CPUs, see
 * __set_cpus_allowed_ptr() and select_fallback_rq().
 */
static inline bool is_cpu_allowed(struct task_struct *p, int cpu)
{
        if (!cpumask_test_cpu(cpu, p->cpus_ptr))
                return false;

        if (is_per_cpu_kthread(p))
                return cpu_online(cpu);

        return cpu_active(cpu);
}

/*
 * This is how migration works:
 *
 * 1) we invoke migration_cpu_stop() on the target CPU using
 *    stop_one_cpu().
 * 2) stopper starts to run (implicitly forcing the migrated thread
 *    off the CPU)
 * 3) it checks whether the migrated task is still in the wrong runqueue.
 * 4) if it's in the wrong runqueue then the migration thread removes
 *    it and puts it into the right queue.
 * 5) stopper completes and stop_one_cpu() returns and the migration
 *    is done.
 */

/*
 * move_queued_task - move a queued task to new rq.
 *
 * Returns (locked) new rq. Old rq's lock is released.
 */
static struct rq *move_queued_task(struct rq *rq, struct rq_flags *rf,
                                   struct task_struct *p, int new_cpu)
{
        lockdep_assert_held(&rq->lock);

        WRITE_ONCE(p->on_rq, TASK_ON_RQ_MIGRATING);
        dequeue_task(rq, p, DEQUEUE_NOCLOCK);
        set_task_cpu(p, new_cpu);
        rq_unlock(rq, rf);

        rq = cpu_rq(new_cpu);

        rq_lock(rq, rf);
        BUG_ON(task_cpu(p) != new_cpu);
        enqueue_task(rq, p, 0);
        p->on_rq = TASK_ON_RQ_QUEUED;
        check_preempt_curr(rq, p, 0);

        return rq;
}

struct migration_arg {
        struct task_struct *task;
        int dest_cpu;
};

/*
 * Move (not current) task off this CPU, onto the destination CPU. We're doing
 * this because either it can't run here any more (set_cpus_allowed()
 * away from this CPU, or CPU going down), or because we're
 * attempting to rebalance this task on exec (sched_exec).
 *
 * So we race with normal scheduler movements, but that's OK, as long
 * as the task is no longer on this CPU.
 */
static struct rq *__migrate_task(struct rq *rq, struct rq_flags *rf,
                                 struct task_struct *p, int dest_cpu)
{
        /* Affinity changed (again). */
        if (!is_cpu_allowed(p, dest_cpu))
                return rq;

        update_rq_clock(rq);
        rq = move_queued_task(rq, rf, p, dest_cpu);

        return rq;
}

/*
 * migration_cpu_stop - this will be executed by a highprio stopper thread
 * and performs thread migration by bumping thread off CPU then
 * 'pushing' onto another runqueue.
 */
static int migration_cpu_stop(void *data)
{
        struct migration_arg *arg = data;
        struct task_struct *p = arg->task;
        struct rq *rq = this_rq();
        struct rq_flags rf;

        /*
         * The original target CPU might have gone down and we might
         * be on another CPU but it doesn't matter.
         */
        local_irq_disable();
        /*
         * We need to explicitly wake pending tasks before running
         * __migrate_task() such that we will not miss enforcing cpus_ptr
         * during wakeups, see set_cpus_allowed_ptr()'s TASK_WAKING test.
         */
        sched_ttwu_pending();

        raw_spin_lock(&p->pi_lock);
        rq_lock(rq, &rf);
        /*
         * If task_rq(p) != rq, it cannot be migrated here, because we're
         * holding rq->lock, if p->on_rq == 0 it cannot get enqueued because
         * we're holding p->pi_lock.
         */
        if (task_rq(p) == rq) {
                if (task_on_rq_queued(p))
                        rq = __migrate_task(rq, &rf, p, arg->dest_cpu);
                else
                        p->wake_cpu = arg->dest_cpu;
        }
        rq_unlock(rq, &rf);
        raw_spin_unlock(&p->pi_lock);

        local_irq_enable();
        return 0;
}

/*
 * sched_class::set_cpus_allowed must do the below, but is not required to
 * actually call this function.
 */
void set_cpus_allowed_common(struct task_struct *p, const struct cpumask *new_mask)
{
        cpumask_copy(&p->cpus_mask, new_mask);
        p->nr_cpus_allowed = cpumask_weight(new_mask);
}

void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
{
        struct rq *rq = task_rq(p);
        bool queued, running;

        lockdep_assert_held(&p->pi_lock);

        queued = task_on_rq_queued(p);
        running = task_current(rq, p);

        if (queued) {
                /*
                 * Because __kthread_bind() calls this on blocked tasks without
                 * holding rq->lock.
                 */
                lockdep_assert_held(&rq->lock);
                dequeue_task(rq, p, DEQUEUE_SAVE | DEQUEUE_NOCLOCK);
        }
        if (running)
                put_prev_task(rq, p);

        p->sched_class->set_cpus_allowed(p, new_mask);

        if (queued)
                enqueue_task(rq, p, ENQUEUE_RESTORE | ENQUEUE_NOCLOCK);
        if (running)
                set_next_task(rq, p);
}

/*
 * Change a given task's CPU affinity. Migrate the thread to a
 * proper CPU and schedule it away if the CPU it's executing on
 * is removed from the allowed bitmask.
 *
 * NOTE: the caller must have a valid reference to the task, the
 * task must not exit() & deallocate itself prematurely. The
 * call is not atomic; no spinlocks may be held.
 */
static int __set_cpus_allowed_ptr(struct task_struct *p,
                                  const struct cpumask *new_mask, bool check)
{
        const struct cpumask *cpu_valid_mask = cpu_active_mask;
        unsigned int dest_cpu;
        struct rq_flags rf;
        struct rq *rq;
        int ret = 0;

        rq = task_rq_lock(p, &rf);
        update_rq_clock(rq);

        if (p->flags & PF_KTHREAD) {
                /*
                 * Kernel threads are allowed on online && !active CPUs
                 */
                cpu_valid_mask = cpu_online_mask;
        }

        /*
         * Must re-check here, to close a race against __kthread_bind(),
         * sched_setaffinity() is not guaranteed to observe the flag.
         */
        if (check && (p->flags & PF_NO_SETAFFINITY)) {
                ret = -EINVAL;
                goto out;
        }

        if (cpumask_equal(p->cpus_ptr, new_mask))
                goto out;

        /*
         * Picking a ~random cpu helps in cases where we are changing affinity
         * for groups of tasks (ie. cpuset), so that load balancing is not
         * immediately required to distribute the tasks within their new mask.
         */
        dest_cpu = cpumask_any_and_distribute(cpu_valid_mask, new_mask);
        if (dest_cpu >= nr_cpu_ids) {
                ret = -EINVAL;
                goto out;
        }

        do_set_cpus_allowed(p, new_mask);

        if (p->flags & PF_KTHREAD) {
                /*
                 * For kernel threads that do indeed end up on online &&
                 * !active we want to ensure they are strict per-CPU threads.
                 */
                WARN_ON(cpumask_intersects(new_mask, cpu_online_mask) &&
                        !cpumask_intersects(new_mask, cpu_active_mask) &&
                        p->nr_cpus_allowed != 1);
        }

        /* Can the task run on the task's current CPU? If so, we're done */
        if (cpumask_test_cpu(task_cpu(p), new_mask))
                goto out;

        if (task_running(rq, p) || p->state == TASK_WAKING) {
                struct migration_arg arg = { p, dest_cpu };
                /* Need help from migration thread: drop lock and wait. */
                task_rq_unlock(rq, p, &rf);
                stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg);
                return 0;
        } else if (task_on_rq_queued(p)) {
                /*
                 * OK, since we're going to drop the lock immediately
                 * afterwards anyway.
                 */
                rq = move_queued_task(rq, &rf, p, dest_cpu);
        }
out:
        task_rq_unlock(rq, p, &rf);

        return ret;
}

int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
{
        return __set_cpus_allowed_ptr(p, new_mask, false);
}
EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr);

void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
{
#ifdef CONFIG_SCHED_DEBUG
        /*
         * We should never call set_task_cpu() on a blocked task,
         * ttwu() will sort out the placement.
         */
        WARN_ON_ONCE(p->state != TASK_RUNNING && p->state != TASK_WAKING &&
                        !p->on_rq);

        /*
         * Migrating fair class task must have p->on_rq = TASK_ON_RQ_MIGRATING,
         * because schedstat_wait_{start,end} rebase migrating task's wait_start
         * time relying on p->on_rq.
         */
        WARN_ON_ONCE(p->state == TASK_RUNNING &&
                     p->sched_class == &fair_sched_class &&
                     (p->on_rq && !task_on_rq_migrating(p)));

#ifdef CONFIG_LOCKDEP
        /*
         * The caller should hold either p->pi_lock or rq->lock, when changing
         * a task's CPU. ->pi_lock for waking tasks, rq->lock for runnable tasks.
         *
         * sched_move_task() holds both and thus holding either pins the cgroup,
         * see task_group().
         *
         * Furthermore, all task_rq users should acquire both locks, see
         * task_rq_lock().
         */
        WARN_ON_ONCE(debug_locks && !(lockdep_is_held(&p->pi_lock) ||
                                      lockdep_is_held(&task_rq(p)->lock)));
#endif
        /*
         * Clearly, migrating tasks to offline CPUs is a fairly daft thing.
         */
        WARN_ON_ONCE(!cpu_online(new_cpu));
#endif

        trace_sched_migrate_task(p, new_cpu);

        if (task_cpu(p) != new_cpu) {
                if (p->sched_class->migrate_task_rq)
                        p->sched_class->migrate_task_rq(p, new_cpu);
                p->se.nr_migrations++;
                rseq_migrate(p);
                perf_event_task_migrate(p);
        }

        __set_task_cpu(p, new_cpu);
}

#ifdef CONFIG_NUMA_BALANCING
static void __migrate_swap_task(struct task_struct *p, int cpu)
{
        if (task_on_rq_queued(p)) {
                struct rq *src_rq, *dst_rq;
                struct rq_flags srf, drf;

                src_rq = task_rq(p);
                dst_rq = cpu_rq(cpu);

                rq_pin_lock(src_rq, &srf);
                rq_pin_lock(dst_rq, &drf);

                deactivate_task(src_rq, p, 0);
                set_task_cpu(p, cpu);
                activate_task(dst_rq, p, 0);
                check_preempt_curr(dst_rq, p, 0);

                rq_unpin_lock(dst_rq, &drf);
                rq_unpin_lock(src_rq, &srf);

        } else {
                /*
                 * Task isn't running anymore; make it appear like we migrated
                 * it before it went to sleep. This means on wakeup we make the
                 * previous CPU our target instead of where it really is.
                 */
                p->wake_cpu = cpu;
        }
}

struct migration_swap_arg {
        struct task_struct *src_task, *dst_task;
        int src_cpu, dst_cpu;
};

static int migrate_swap_stop(void *data)
{
        struct migration_swap_arg *arg = data;
        struct rq *src_rq, *dst_rq;
        int ret = -EAGAIN;

        if (!cpu_active(arg->src_cpu) || !cpu_active(arg->dst_cpu))
                return -EAGAIN;

        src_rq = cpu_rq(arg->src_cpu);
        dst_rq = cpu_rq(arg->dst_cpu);

        double_raw_lock(&arg->src_task->pi_lock,
                        &arg->dst_task->pi_lock);
        double_rq_lock(src_rq, dst_rq);

        if (task_cpu(arg->dst_task) != arg->dst_cpu)
                goto unlock;

        if (task_cpu(arg->src_task) != arg->src_cpu)
                goto unlock;

        if (!cpumask_test_cpu(arg->dst_cpu, arg->src_task->cpus_ptr))
                goto unlock;

        if (!cpumask_test_cpu(arg->src_cpu, arg->dst_task->cpus_ptr))
                goto unlock;

        __migrate_swap_task(arg->src_task, arg->dst_cpu);
        __migrate_swap_task(arg->dst_task, arg->src_cpu);

        ret = 0;

unlock:
        double_rq_unlock(src_rq, dst_rq);
        raw_spin_unlock(&arg->dst_task->pi_lock);
        raw_spin_unlock(&arg->src_task->pi_lock);

        return ret;
}

/*
 * Cross migrate two tasks
 */
int migrate_swap(struct task_struct *cur, struct task_struct *p,
                int target_cpu, int curr_cpu)
{
        struct migration_swap_arg arg;
        int ret = -EINVAL;

        arg = (struct migration_swap_arg){
                .src_task = cur,
                .src_cpu = curr_cpu,
                .dst_task = p,
                .dst_cpu = target_cpu,
        };

        if (arg.src_cpu == arg.dst_cpu)
                goto out;

        /*
         * These three tests are all lockless; this is OK since all of them
         * will be re-checked with proper locks held further down the line.
         */
        if (!cpu_active(arg.src_cpu) || !cpu_active(arg.dst_cpu))
                goto out;

        if (!cpumask_test_cpu(arg.dst_cpu, arg.src_task->cpus_ptr))
                goto out;

        if (!cpumask_test_cpu(arg.src_cpu, arg.dst_task->cpus_ptr))
                goto out;

        trace_sched_swap_numa(cur, arg.src_cpu, p, arg.dst_cpu);
        ret = stop_two_cpus(arg.dst_cpu, arg.src_cpu, migrate_swap_stop, &arg);

out:
        return ret;
}
#endif /* CONFIG_NUMA_BALANCING */

/*
 * wait_task_inactive - wait for a thread to unschedule.
 *
 * If @match_state is nonzero, it's the @p->state value just checked and
 * not expected to change.  If it changes, i.e. @p might have woken up,
 * then return zero.  When we succeed in waiting for @p to be off its CPU,
 * we return a positive number (its total switch count).  If a second call
 * a short while later returns the same number, the caller can be sure that
 * @p has remained unscheduled the whole time.
 *
 * The caller must ensure that the task *will* unschedule sometime soon,
 * else this function might spin for a *long* time. This function can't
 * be called with interrupts off, or it may introduce deadlock with
 * smp_call_function() if an IPI is sent by the same process we are
 * waiting to become inactive.
 */
unsigned long wait_task_inactive(struct task_struct *p, long match_state)
{
        int running, queued;
        struct rq_flags rf;
        unsigned long ncsw;
        struct rq *rq;

        for (;;) {
                /*
                 * We do the initial early heuristics without holding
                 * any task-queue locks at all. We'll only try to get
                 * the runqueue lock when things look like they will
                 * work out!
                 */
                rq = task_rq(p);

                /*
                 * If the task is actively running on another CPU
                 * still, just relax and busy-wait without holding
                 * any locks.
                 *
                 * NOTE! Since we don't hold any locks, it's not
                 * even sure that "rq" stays as the right runqueue!
                 * But we don't care, since "task_running()" will
                 * return false if the runqueue has changed and p
                 * is actually now running somewhere else!
                 */
                while (task_running(rq, p)) {
                        if (match_state && unlikely(p->state != match_state))
                                return 0;
                        cpu_relax();
                }

                /*
                 * Ok, time to look more closely! We need the rq
                 * lock now, to be *sure*. If we're wrong, we'll
                 * just go back and repeat.
                 */
                rq = task_rq_lock(p, &rf);
                trace_sched_wait_task(p);
                running = task_running(rq, p);
                queued = task_on_rq_queued(p);
                ncsw = 0;
                if (!match_state || p->state == match_state)
                        ncsw = p->nvcsw | LONG_MIN; /* sets MSB */
                task_rq_unlock(rq, p, &rf);

                /*
                 * If it changed from the expected state, bail out now.
                 */
                if (unlikely(!ncsw))
                        break;

                /*
                 * Was it really running after all now that we
                 * checked with the proper locks actually held?
                 *
                 * Oops. Go back and try again..
                 */
                if (unlikely(running)) {
                        cpu_relax();
                        continue;
                }

                /*
                 * It's not enough that it's not actively running,
                 * it must be off the runqueue _entirely_, and not
                 * preempted!
                 *
                 * So if it was still runnable (but just not actively
                 * running right now), it's preempted, and we should
                 * yield - it could be a while.
                 */
                if (unlikely(queued)) {
                        ktime_t to = NSEC_PER_SEC / HZ;

                        set_current_state(TASK_UNINTERRUPTIBLE);
                        schedule_hrtimeout(&to, HRTIMER_MODE_REL);
                        continue;
                }

                /*
                 * Ahh, all good. It wasn't running, and it wasn't
                 * runnable, which means that it will never become
                 * running in the future either. We're all done!
                 */
                break;
        }

        return ncsw;
}

/***
 * kick_process - kick a running thread to enter/exit the kernel
 * @p: the to-be-kicked thread
 *
 * Cause a process which is running on another CPU to enter
 * kernel-mode, without any delay. (to get signals handled.)
 *
 * NOTE: this function doesn't have to take the runqueue lock,
 * because all it wants to ensure is that the remote task enters
 * the kernel. If the IPI races and the task has been migrated
 * to another CPU then no harm is done and the purpose has been
 * achieved as well.
 */
void kick_process(struct task_struct *p)
{
        int cpu;

        preempt_disable();
        cpu = task_cpu(p);
        if ((cpu != smp_processor_id()) && task_curr(p))
                smp_send_reschedule(cpu);
        preempt_enable();
}
EXPORT_SYMBOL_GPL(kick_process);

/*
 * ->cpus_ptr is protected by both rq->lock and p->pi_lock
 *
 * A few notes on cpu_active vs cpu_online:
 *
 *  - cpu_active must be a subset of cpu_online
 *
 *  - on CPU-up we allow per-CPU kthreads on the online && !active CPU,
 *    see __set_cpus_allowed_ptr(). At this point the newly online
 *    CPU isn't yet part of the sched domains, and balancing will not
 *    see it.
 *
 *  - on CPU-down we clear cpu_active() to mask the sched domains and
 *    avoid the load balancer to place new tasks on the to be removed
 *    CPU. Existing tasks will remain running there and will be taken
 *    off.
 *
 * This means that fallback selection must not select !active CPUs.
 * And can assume that any active CPU must be online. Conversely
 * select_task_rq() below may allow selection of !active CPUs in order
 * to satisfy the above rules.
 */
static int select_fallback_rq(int cpu, struct task_struct *p)
{
        int nid = cpu_to_node(cpu);
        const struct cpumask *nodemask = NULL;
        enum { cpuset, possible, fail } state = cpuset;
        int dest_cpu;

        /*
         * If the node that the CPU is on has been offlined, cpu_to_node()
         * will return -1. There is no CPU on the node, and we should
         * select the CPU on the other node.
         */
        if (nid != -1) {
                nodemask = cpumask_of_node(nid);

                /* Look for allowed, online CPU in same node. */
                for_each_cpu(dest_cpu, nodemask) {
                        if (!cpu_active(dest_cpu))
                                continue;
                        if (cpumask_test_cpu(dest_cpu, p->cpus_ptr))
                                return dest_cpu;
                }
        }

        for (;;) {
                /* Any allowed, online CPU? */
                for_each_cpu(dest_cpu, p->cpus_ptr) {
                        if (!is_cpu_allowed(p, dest_cpu))
                                continue;

                        goto out;
                }

                /* No more Mr. Nice Guy. */
                switch (state) {
                case cpuset:
                        if (IS_ENABLED(CONFIG_CPUSETS)) {
                                cpuset_cpus_allowed_fallback(p);
                                state = possible;
                                break;
                        }
                        /* Fall-through */
                case possible:
                        do_set_cpus_allowed(p, cpu_possible_mask);
                        state = fail;
                        break;

                case fail:
                        BUG();
                        break;
                }
        }

out:
        if (state != cpuset) {
                /*
                 * Don't tell them about moving exiting tasks or
                 * kernel threads (both mm NULL), since they never
                 * leave kernel.
                 */
                if (p->mm && printk_ratelimit()) {
                        printk_deferred("process %d (%s) no longer affine to cpu%d\n",
                                        task_pid_nr(p), p->comm, cpu);
                }
        }

        return dest_cpu;
}

/*
 * The caller (fork, wakeup) owns p->pi_lock, ->cpus_ptr is stable.
 */
static inline
int select_task_rq(struct task_struct *p, int cpu, int sd_flags, int wake_flags)
{
        lockdep_assert_held(&p->pi_lock);

        if (p->nr_cpus_allowed > 1)
                cpu = p->sched_class->select_task_rq(p, cpu, sd_flags, wake_flags);
        else
                cpu = cpumask_any(p->cpus_ptr);

        /*
         * In order not to call set_task_cpu() on a blocking task we need
         * to rely on ttwu() to place the task on a valid ->cpus_ptr
         * CPU.
         *
         * Since this is common to all placement strategies, this lives here.
         *
         * [ this allows ->select_task() to simply return task_cpu(p) and
         *   not worry about this generic constraint ]
         */
        if (unlikely(!is_cpu_allowed(p, cpu)))
                cpu = select_fallback_rq(task_cpu(p), p);

        return cpu;
}

void sched_set_stop_task(int cpu, struct task_struct *stop)
{
        struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 };
        struct task_struct *old_stop = cpu_rq(cpu)->stop;

        if (stop) {
                /*
                 * Make it appear like a SCHED_FIFO task, its something
                 * userspace knows about and won't get confused about.
                 *
                 * Also, it will make PI more or less work without too
                 * much confusion -- but then, stop work should not
                 * rely on PI working anyway.
                 */
                sched_setscheduler_nocheck(stop, SCHED_FIFO, &param);

                stop->sched_class = &stop_sched_class;
        }

        cpu_rq(cpu)->stop = stop;

        if (old_stop) {
                /*
                 * Reset it back to a normal scheduling class so that
                 * it can die in pieces.
                 */
                old_stop->sched_class = &rt_sched_class;
        }
}

#else

static inline int __set_cpus_allowed_ptr(struct task_struct *p,
                                         const struct cpumask *new_mask, bool check)
{
        return set_cpus_allowed_ptr(p, new_mask);
}

#endif /* CONFIG_SMP */

static void
ttwu_stat(struct task_struct *p, int cpu, int wake_flags)
{
        struct rq *rq;

        if (!schedstat_enabled())
                return;

        rq = this_rq();

#ifdef CONFIG_SMP
        if (cpu == rq->cpu) {
                __schedstat_inc(rq->ttwu_local);
                __schedstat_inc(p->se.statistics.nr_wakeups_local);
        } else {
                struct sched_domain *sd;

                __schedstat_inc(p->se.statistics.nr_wakeups_remote);
                rcu_read_lock();
                for_each_domain(rq->cpu, sd) {
                        if (cpumask_test_cpu(cpu, sched_domain_span(sd))) {
                                __schedstat_inc(sd->ttwu_wake_remote);
                                break;
                        }
                }
                rcu_read_unlock();
        }

        if (wake_flags & WF_MIGRATED)
                __schedstat_inc(p->se.statistics.nr_wakeups_migrate);
#endif /* CONFIG_SMP */

        __schedstat_inc(rq->ttwu_count);
        __schedstat_inc(p->se.statistics.nr_wakeups);

        if (wake_flags & WF_SYNC)
                __schedstat_inc(p->se.statistics.nr_wakeups_sync);
}

/*
 * Mark the task runnable and perform wakeup-preemption.
 */
static void ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags,
                           struct rq_flags *rf)
{
        check_preempt_curr(rq, p, wake_flags);
        p->state = TASK_RUNNING;
        trace_sched_wakeup(p);

#ifdef CONFIG_SMP
        if (p->sched_class->task_woken) {
                /*
                 * Our task @p is fully woken up and running; so its safe to
                 * drop the rq->lock, hereafter rq is only used for statistics.
                 */
                rq_unpin_lock(rq, rf);
                p->sched_class->task_woken(rq, p);
                rq_repin_lock(rq, rf);
        }

        if (rq->idle_stamp) {
                u64 delta = rq_clock(rq) - rq->idle_stamp;
                u64 max = 2*rq->max_idle_balance_cost;

                update_avg(&rq->avg_idle, delta);

                if (rq->avg_idle > max)
                        rq->avg_idle = max;

                rq->idle_stamp = 0;
        }
#endif
}

static void
ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags,
                 struct rq_flags *rf)
{
        int en_flags = ENQUEUE_WAKEUP | ENQUEUE_NOCLOCK;

        lockdep_assert_held(&rq->lock);

#ifdef CONFIG_SMP
        if (p->sched_contributes_to_load)
                rq->nr_uninterruptible--;

        if (wake_flags & WF_MIGRATED)
                en_flags |= ENQUEUE_MIGRATED;
#endif

        activate_task(rq, p, en_flags);
        ttwu_do_wakeup(rq, p, wake_flags, rf);
}

/*
 * Called in case the task @p isn't fully descheduled from its runqueue,
 * in this case we must do a remote wakeup. Its a 'light' wakeup though,
 * since all we need to do is flip p->state to TASK_RUNNING, since
 * the task is still ->on_rq.
 */
static int ttwu_remote(struct task_struct *p, int wake_flags)
{
        struct rq_flags rf;
        struct rq *rq;
        int ret = 0;

        rq = __task_rq_lock(p, &rf);
        if (task_on_rq_queued(p)) {
                /* check_preempt_curr() may use rq clock */
                update_rq_clock(rq);
                ttwu_do_wakeup(rq, p, wake_flags, &rf);
                ret = 1;
        }
        __task_rq_unlock(rq, &rf);

        return ret;
}

#ifdef CONFIG_SMP
void sched_ttwu_pending(void)
{
        struct rq *rq = this_rq();
        struct llist_node *llist = llist_del_all(&rq->wake_list);
        struct task_struct *p, *t;
        struct rq_flags rf;

        if (!llist)
                return;

        rq_lock_irqsave(rq, &rf);
        update_rq_clock(rq);

        llist_for_each_entry_safe(p, t, llist, wake_entry)
                ttwu_do_activate(rq, p, p->sched_remote_wakeup ? WF_MIGRATED : 0, &rf);

        rq_unlock_irqrestore(rq, &rf);
}

static void wake_csd_func(void *info)
{
        sched_ttwu_pending();
}

void scheduler_ipi(void)
{
        /*
         * Fold TIF_NEED_RESCHED into the preempt_count; anybody setting
         * TIF_NEED_RESCHED remotely (for the first time) will also send
         * this IPI.
         */
        preempt_fold_need_resched();
}

static void ttwu_queue_remote(struct task_struct *p, int cpu, int wake_flags)
{
        struct rq *rq = cpu_rq(cpu);

        p->sched_remote_wakeup = !!(wake_flags & WF_MIGRATED);

        if (llist_add(&p->wake_entry, &rq->wake_list)) {
                if (!set_nr_if_polling(rq->idle))
                        smp_call_function_single_async(cpu, &rq->wake_csd);
                else
                        trace_sched_wake_idle_without_ipi(cpu);
        }
}

void wake_up_if_idle(int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        struct rq_flags rf;

        rcu_read_lock();

        if (!is_idle_task(rcu_dereference(rq->curr)))
                goto out;

        if (set_nr_if_polling(rq->idle)) {
                trace_sched_wake_idle_without_ipi(cpu);
        } else {
                rq_lock_irqsave(rq, &rf);
                if (is_idle_task(rq->curr))
                        smp_send_reschedule(cpu);
                /* Else CPU is not idle, do nothing here: */
                rq_unlock_irqrestore(rq, &rf);
        }

out:
        rcu_read_unlock();
}

bool cpus_share_cache(int this_cpu, int that_cpu)
{
        return per_cpu(sd_llc_id, this_cpu) == per_cpu(sd_llc_id, that_cpu);
}
#endif /* CONFIG_SMP */

static void ttwu_queue(struct task_struct *p, int cpu, int wake_flags)
{
        struct rq *rq = cpu_rq(cpu);
        struct rq_flags rf;

#if defined(CONFIG_SMP)
        if (sched_feat(TTWU_QUEUE) && !cpus_share_cache(smp_processor_id(), cpu)) {
                sched_clock_cpu(cpu); /* Sync clocks across CPUs */
                ttwu_queue_remote(p, cpu, wake_flags);
                return;
        }
#endif

        rq_lock(rq, &rf);
        update_rq_clock(rq);
        ttwu_do_activate(rq, p, wake_flags, &rf);
        rq_unlock(rq, &rf);
}

/*
 * Notes on Program-Order guarantees on SMP systems.
 *
 *  MIGRATION
 *
 * The basic program-order guarantee on SMP systems is that when a task [t]
 * migrates, all its activity on its old CPU [c0] happens-before any subsequent
 * execution on its new CPU [c1].
 *
 * For migration (of runnable tasks) this is provided by the following means:
 *
 *  A) UNLOCK of the rq(c0)->lock scheduling out task t
 *  B) migration for t is required to synchronize *both* rq(c0)->lock and
 *     rq(c1)->lock (if not at the same time, then in that order).
 *  C) LOCK of the rq(c1)->lock scheduling in task
 *
 * Release/acquire chaining guarantees that B happens after A and C after B.
 * Note: the CPU doing B need not be c0 or c1
 *
 * Example:
 *
 *   CPU0            CPU1            CPU2
 *
 *   LOCK rq(0)->lock
 *   sched-out X
 *   sched-in Y
 *   UNLOCK rq(0)->lock
 *
 *                                   LOCK rq(0)->lock // orders against CPU0
 *                                   dequeue X
 *                                   UNLOCK rq(0)->lock
 *
 *                                   LOCK rq(1)->lock
 *                                   enqueue X
 *                                   UNLOCK rq(1)->lock
 *
 *                   LOCK rq(1)->lock // orders against CPU2
 *                   sched-out Z
 *                   sched-in X
 *                   UNLOCK rq(1)->lock
 *
 *
 *  BLOCKING -- aka. SLEEP + WAKEUP
 *
 * For blocking we (obviously) need to provide the same guarantee as for
 * migration. However the means are completely different as there is no lock
 * chain to provide order. Instead we do:
 *
 *   1) smp_store_release(X->on_cpu, 0)
 *   2) smp_cond_load_acquire(!X->on_cpu)
 *
 * Example:
 *
 *   CPU0 (schedule)  CPU1 (try_to_wake_up) CPU2 (schedule)
 *
 *   LOCK rq(0)->lock LOCK X->pi_lock
 *   dequeue X
 *   sched-out X
 *   smp_store_release(X->on_cpu, 0);
 *
 *                    smp_cond_load_acquire(&X->on_cpu, !VAL);
 *                    X->state = WAKING
 *                    set_task_cpu(X,2)
 *
 *                    LOCK rq(2)->lock
 *                    enqueue X
 *                    X->state = RUNNING
 *                    UNLOCK rq(2)->lock
 *
 *                                          LOCK rq(2)->lock // orders against CPU1
 *                                          sched-out Z
 *                                          sched-in X
 *                                          UNLOCK rq(2)->lock
 *
 *                    UNLOCK X->pi_lock
 *   UNLOCK rq(0)->lock
 *
 *
 * However, for wakeups there is a second guarantee we must provide, namely we
 * must ensure that CONDITION=1 done by the caller can not be reordered with
 * accesses to the task state; see try_to_wake_up() and set_current_state().
 */

/**
 * try_to_wake_up - wake up a thread
 * @p: the thread to be awakened
 * @state: the mask of task states that can be woken
 * @wake_flags: wake modifier flags (WF_*)
 *
 * If (@state & @p->state) @p->state = TASK_RUNNING.
 *
 * If the task was not queued/runnable, also place it back on a runqueue.
 *
 * Atomic against schedule() which would dequeue a task, also see
 * set_current_state().
 *
 * This function executes a full memory barrier before accessing the task
 * state; see set_current_state().
 *
 * Return: %true if @p->state changes (an actual wakeup was done),
 *         %false otherwise.
 */
static int
try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
{
        unsigned long flags;
        int cpu, success = 0;

        preempt_disable();
        if (p == current) {
                /*
                 * We're waking current, this means 'p->on_rq' and 'task_cpu(p)
                 * == smp_processor_id()'. Together this means we can special
                 * case the whole 'p->on_rq && ttwu_remote()' case below
                 * without taking any locks.
                 *
                 * In particular:
                 *  - we rely on Program-Order guarantees for all the ordering,
                 *  - we're serialized against set_special_state() by virtue of
                 *    it disabling IRQs (this allows not taking ->pi_lock).
                 */
                if (!(p->state & state))
                        goto out;

                success = 1;
                cpu = task_cpu(p);
                trace_sched_waking(p);
                p->state = TASK_RUNNING;
                trace_sched_wakeup(p);
                goto out;
        }

        /*
         * If we are going to wake up a thread waiting for CONDITION we
         * need to ensure that CONDITION=1 done by the caller can not be
         * reordered with p->state check below. This pairs with mb() in
         * set_current_state() the waiting thread does.
         */
        raw_spin_lock_irqsave(&p->pi_lock, flags);
        smp_mb__after_spinlock();
        if (!(p->state & state))
                goto unlock;

        trace_sched_waking(p);

        /* We're going to change ->state: */
        success = 1;
        cpu = task_cpu(p);

        /*
         * Ensure we load p->on_rq _after_ p->state, otherwise it would
         * be possible to, falsely, observe p->on_rq == 0 and get stuck
         * in smp_cond_load_acquire() below.
         *
         * sched_ttwu_pending()                 try_to_wake_up()
         *   STORE p->on_rq = 1                   LOAD p->state
         *   UNLOCK rq->lock
         *
         * __schedule() (switch to task 'p')
         *   LOCK rq->lock                        smp_rmb();
         *   smp_mb__after_spinlock();
         *   UNLOCK rq->lock
         *
         * [task p]
         *   STORE p->state = UNINTERRUPTIBLE     LOAD p->on_rq
         *
         * Pairs with the LOCK+smp_mb__after_spinlock() on rq->lock in
         * __schedule().  See the comment for smp_mb__after_spinlock().
         */
        smp_rmb();
        if (p->on_rq && ttwu_remote(p, wake_flags))
                goto unlock;

#ifdef CONFIG_SMP
        /*
         * Ensure we load p->on_cpu _after_ p->on_rq, otherwise it would be
         * possible to, falsely, observe p->on_cpu == 0.
         *
         * One must be running (->on_cpu == 1) in order to remove oneself
         * from the runqueue.
         *
         * __schedule() (switch to task 'p')    try_to_wake_up()
         *   STORE p->on_cpu = 1                  LOAD p->on_rq
         *   UNLOCK rq->lock
         *
         * __schedule() (put 'p' to sleep)
         *   LOCK rq->lock                        smp_rmb();
         *   smp_mb__after_spinlock();
         *   STORE p->on_rq = 0                   LOAD p->on_cpu
         *
         * Pairs with the LOCK+smp_mb__after_spinlock() on rq->lock in
         * __schedule().  See the comment for smp_mb__after_spinlock().
         */
        smp_rmb();

        /*
         * If the owning (remote) CPU is still in the middle of schedule() with
         * this task as prev, wait until its done referencing the task.
         *
         * Pairs with the smp_store_release() in finish_task().
         *
         * This ensures that tasks getting woken will be fully ordered against
         * their previous state and preserve Program Order.
         */
        smp_cond_load_acquire(&p->on_cpu, !VAL);

        p->sched_contributes_to_load = !!task_contributes_to_load(p);
        p->state = TASK_WAKING;

        if (p->in_iowait) {
                delayacct_blkio_end(p);
                atomic_dec(&task_rq(p)->nr_iowait);
        }

        cpu = select_task_rq(p, p->wake_cpu, SD_BALANCE_WAKE, wake_flags);
        if (task_cpu(p) != cpu) {
                wake_flags |= WF_MIGRATED;
                psi_ttwu_dequeue(p);
                set_task_cpu(p, cpu);
        }

#else /* CONFIG_SMP */

        if (p->in_iowait) {
                delayacct_blkio_end(p);
                atomic_dec(&task_rq(p)->nr_iowait);
        }

#endif /* CONFIG_SMP */

        ttwu_queue(p, cpu, wake_flags);
unlock:
        raw_spin_unlock_irqrestore(&p->pi_lock, flags);
out:
        if (success)
                ttwu_stat(p, cpu, wake_flags);
        preempt_enable();

        return success;
}

/**
 * wake_up_process - Wake up a specific process
 * @p: The process to be woken up.
 *
 * Attempt to wake up the nominated process and move it to the set of runnable
 * processes.
 *
 * Return: 1 if the process was woken up, 0 if it was already running.
 *
 * This function executes a full memory barrier before accessing the task state.
 */
int wake_up_process(struct task_struct *p)
{
        return try_to_wake_up(p, TASK_NORMAL, 0);
}
EXPORT_SYMBOL(wake_up_process);

int wake_up_state(struct task_struct *p, unsigned int state)
{
        return try_to_wake_up(p, state, 0);
}

/*
 * Perform scheduler related setup for a newly forked process p.
 * p is forked by current.
 *
 * __sched_fork() is basic setup used by init_idle() too:
 */
static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
{
        p->on_rq                        = 0;

        p->se.on_rq                     = 0;
        p->se.exec_start                = 0;
        p->se.sum_exec_runtime          = 0;
        p->se.prev_sum_exec_runtime     = 0;
        p->se.nr_migrations             = 0;
        p->se.vruntime                  = 0;
        INIT_LIST_HEAD(&p->se.group_node);

#ifdef CONFIG_FAIR_GROUP_SCHED
        p->se.cfs_rq                    = NULL;
#endif

#ifdef CONFIG_SCHEDSTATS
        /* Even if schedstat is disabled, there should not be garbage */
        memset(&p->se.statistics, 0, sizeof(p->se.statistics));
#endif

        RB_CLEAR_NODE(&p->dl.rb_node);
        init_dl_task_timer(&p->dl);
        init_dl_inactive_task_timer(&p->dl);
        __dl_clear_params(p);

        INIT_LIST_HEAD(&p->rt.run_list);
        p->rt.timeout           = 0;
        p->rt.time_slice        = sched_rr_timeslice;
        p->rt.on_rq             = 0;
        p->rt.on_list           = 0;

#ifdef CONFIG_PREEMPT_NOTIFIERS
        INIT_HLIST_HEAD(&p->preempt_notifiers);
#endif

#ifdef CONFIG_COMPACTION
        p->capture_control = NULL;
#endif
        init_numa_balancing(clone_flags, p);
}

DEFINE_STATIC_KEY_FALSE(sched_numa_balancing);

#ifdef CONFIG_NUMA_BALANCING

void set_numabalancing_state(bool enabled)
{
        if (enabled)
                static_branch_enable(&sched_numa_balancing);
        else
                static_branch_disable(&sched_numa_balancing);
}

#ifdef CONFIG_PROC_SYSCTL
int sysctl_numa_balancing(struct ctl_table *table, int write,
                         void __user *buffer, size_t *lenp, loff_t *ppos)
{
        struct ctl_table t;
        int err;
        int state = static_branch_likely(&sched_numa_balancing);

        if (write && !capable(CAP_SYS_ADMIN))
                return -EPERM;

        t = *table;
        t.data = &state;
        err = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
        if (err < 0)
                return err;
        if (write)
                set_numabalancing_state(state);
        return err;
}
#endif
#endif

#ifdef CONFIG_SCHEDSTATS

DEFINE_STATIC_KEY_FALSE(sched_schedstats);
static bool __initdata __sched_schedstats = false;

static void set_schedstats(bool enabled)
{
        if (enabled)
                static_branch_enable(&sched_schedstats);
        else
                static_branch_disable(&sched_schedstats);
}

void force_schedstat_enabled(void)
{
        if (!schedstat_enabled()) {
                pr_info("kernel profiling enabled schedstats, disable via kernel.sched_schedstats.\n");
                static_branch_enable(&sched_schedstats);
        }
}

static int __init setup_schedstats(char *str)
{
        int ret = 0;
        if (!str)
                goto out;

        /*
         * This code is called before jump labels have been set up, so we can't
         * change the static branch directly just yet.  Instead set a temporary
         * variable so init_schedstats() can do it later.
         */
        if (!strcmp(str, "enable")) {
                __sched_schedstats = true;
                ret = 1;
        } else if (!strcmp(str, "disable")) {
                __sched_schedstats = false;
                ret = 1;
        }
out:
        if (!ret)
                pr_warn("Unable to parse schedstats=\n");

        return ret;
}
__setup("schedstats=", setup_schedstats);

static void __init init_schedstats(void)
{
        set_schedstats(__sched_schedstats);
}

#ifdef CONFIG_PROC_SYSCTL
int sysctl_schedstats(struct ctl_table *table, int write,
                         void __user *buffer, size_t *lenp, loff_t *ppos)
{
        struct ctl_table t;
        int err;
        int state = static_branch_likely(&sched_schedstats);

        if (write && !capable(CAP_SYS_ADMIN))
                return -EPERM;

        t = *table;
        t.data = &state;
        err = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
        if (err < 0)
                return err;
        if (write)
                set_schedstats(state);
        return err;
}
#endif /* CONFIG_PROC_SYSCTL */
#else  /* !CONFIG_SCHEDSTATS */
static inline void init_schedstats(void) {}
#endif /* CONFIG_SCHEDSTATS */

/*
 * fork()/clone()-time setup:
 */
int sched_fork(unsigned long clone_flags, struct task_struct *p)
{
        unsigned long flags;

        __sched_fork(clone_flags, p);
        /*
         * We mark the process as NEW here. This guarantees that
         * nobody will actually run it, and a signal or other external
         * event cannot wake it up and insert it on the runqueue either.
         */
        p->state = TASK_NEW;

        /*
         * Make sure we do not leak PI boosting priority to the child.
         */
        p->prio = current->normal_prio;

        uclamp_fork(p);

        /*
         * Revert to default priority/policy on fork if requested.
         */
        if (unlikely(p->sched_reset_on_fork)) {
                if (task_has_dl_policy(p) || task_has_rt_policy(p)) {
                        p->policy = SCHED_NORMAL;
                        p->static_prio = NICE_TO_PRIO(0);
                        p->rt_priority = 0;
                } else if (PRIO_TO_NICE(p->static_prio) < 0)
                        p->static_prio = NICE_TO_PRIO(0);

                p->prio = p->normal_prio = __normal_prio(p);
                set_load_weight(p, false);

                /*
                 * We don't need the reset flag anymore after the fork. It has
                 * fulfilled its duty:
                 */
                p->sched_reset_on_fork = 0;
        }

        if (dl_prio(p->prio))
                return -EAGAIN;
        else if (rt_prio(p->prio))
                p->sched_class = &rt_sched_class;
        else
                p->sched_class = &fair_sched_class;

        init_entity_runnable_average(&p->se);

        /*
         * The child is not yet in the pid-hash so no cgroup attach races,
         * and the cgroup is pinned to this child due to cgroup_fork()
         * is ran before sched_fork().
         *
         * Silence PROVE_RCU.
         */
        raw_spin_lock_irqsave(&p->pi_lock, flags);
        /*
         * We're setting the CPU for the first time, we don't migrate,
         * so use __set_task_cpu().
         */
        __set_task_cpu(p, smp_processor_id());
        if (p->sched_class->task_fork)
                p->sched_class->task_fork(p);
        raw_spin_unlock_irqrestore(&p->pi_lock, flags);

#ifdef CONFIG_SCHED_INFO
        if (likely(sched_info_on()))
                memset(&p->sched_info, 0, sizeof(p->sched_info));
#endif
#if defined(CONFIG_SMP)
        p->on_cpu = 0;
#endif
        init_task_preempt_count(p);
#ifdef CONFIG_SMP
        plist_node_init(&p->pushable_tasks, MAX_PRIO);
        RB_CLEAR_NODE(&p->pushable_dl_tasks);
#endif
        return 0;
}

unsigned long to_ratio(u64 period, u64 runtime)
{
        if (runtime == RUNTIME_INF)
                return BW_UNIT;

        /*
         * Doing this here saves a lot of checks in all
         * the calling paths, and returning zero seems
         * safe for them anyway.
         */
        if (period == 0)
                return 0;

        return div64_u64(runtime << BW_SHIFT, period);
}

/*
 * wake_up_new_task - wake up a newly created task for the first time.
 *
 * This function will do some initial scheduler statistics housekeeping
 * that must be done for every newly created context, then puts the task
 * on the runqueue and wakes it.
 */
void wake_up_new_task(struct task_struct *p)
{
        struct rq_flags rf;
        struct rq *rq;

        raw_spin_lock_irqsave(&p->pi_lock, rf.flags);
        p->state = TASK_RUNNING;
#ifdef CONFIG_SMP
        /*
         * Fork balancing, do it here and not earlier because:
         *  - cpus_ptr can change in the fork path
         *  - any previously selected CPU might disappear through hotplug
         *
         * Use __set_task_cpu() to avoid calling sched_class::migrate_task_rq,
         * as we're not fully set-up yet.
         */
        p->recent_used_cpu = task_cpu(p);
        __set_task_cpu(p, select_task_rq(p, task_cpu(p), SD_BALANCE_FORK, 0));
#endif
        rq = __task_rq_lock(p, &rf);
        update_rq_clock(rq);
        post_init_entity_util_avg(p);

        activate_task(rq, p, ENQUEUE_NOCLOCK);
        trace_sched_wakeup_new(p);
        check_preempt_curr(rq, p, WF_FORK);
#ifdef CONFIG_SMP
        if (p->sched_class->task_woken) {
                /*
                 * Nothing relies on rq->lock after this, so its fine to
                 * drop it.
                 */
                rq_unpin_lock(rq, &rf);
                p->sched_class->task_woken(rq, p);
                rq_repin_lock(rq, &rf);
        }
#endif
        task_rq_unlock(rq, p, &rf);
}

#ifdef CONFIG_PREEMPT_NOTIFIERS

static DEFINE_STATIC_KEY_FALSE(preempt_notifier_key);

void preempt_notifier_inc(void)
{
        static_branch_inc(&preempt_notifier_key);
}
EXPORT_SYMBOL_GPL(preempt_notifier_inc);

void preempt_notifier_dec(void)
{
        static_branch_dec(&preempt_notifier_key);
}
EXPORT_SYMBOL_GPL(preempt_notifier_dec);

/**
 * preempt_notifier_register - tell me when current is being preempted & rescheduled
 * @notifier: notifier struct to register
 */
void preempt_notifier_register(struct preempt_notifier *notifier)
{
        if (!static_branch_unlikely(&preempt_notifier_key))
                WARN(1, "registering preempt_notifier while notifiers disabled\n");

        hlist_add_head(&notifier->link, &current->preempt_notifiers);
}
EXPORT_SYMBOL_GPL(preempt_notifier_register);

/**
 * preempt_notifier_unregister - no longer interested in preemption notifications
 * @notifier: notifier struct to unregister
 *
 * This is *not* safe to call from within a preemption notifier.
 */
void preempt_notifier_unregister(struct preempt_notifier *notifier)
{
        hlist_del(&notifier->link);
}
EXPORT_SYMBOL_GPL(preempt_notifier_unregister);

static void __fire_sched_in_preempt_notifiers(struct task_struct *curr)
{
        struct preempt_notifier *notifier;

        hlist_for_each_entry(notifier, &curr->preempt_notifiers, link)
                notifier->ops->sched_in(notifier, raw_smp_processor_id());
}

static __always_inline void fire_sched_in_preempt_notifiers(struct task_struct *curr)
{
        if (static_branch_unlikely(&preempt_notifier_key))
                __fire_sched_in_preempt_notifiers(curr);
}

static void
__fire_sched_out_preempt_notifiers(struct task_struct *curr,
                                   struct task_struct *next)
{
        struct preempt_notifier *notifier;

        hlist_for_each_entry(notifier, &curr->preempt_notifiers, link)
                notifier->ops->sched_out(notifier, next);
}

static __always_inline void
fire_sched_out_preempt_notifiers(struct task_struct *curr,
                                 struct task_struct *next)
{
        if (static_branch_unlikely(&preempt_notifier_key))
                __fire_sched_out_preempt_notifiers(curr, next);
}

#else /* !CONFIG_PREEMPT_NOTIFIERS */

static inline void fire_sched_in_preempt_notifiers(struct task_struct *curr)
{
}

static inline void
fire_sched_out_preempt_notifiers(struct task_struct *curr,
                                 struct task_struct *next)
{
}

#endif /* CONFIG_PREEMPT_NOTIFIERS */

static inline void prepare_task(struct task_struct *next)
{
#ifdef CONFIG_SMP
        /*
         * Claim the task as running, we do this before switching to it
         * such that any running task will have this set.
         */
        next->on_cpu = 1;
#endif
}

static inline void finish_task(struct task_struct *prev)
{
#ifdef CONFIG_SMP
        /*
         * After ->on_cpu is cleared, the task can be moved to a different CPU.
         * We must ensure this doesn't happen until the switch is completely
         * finished.
         *
         * In particular, the load of prev->state in finish_task_switch() must
         * happen before this.
         *
         * Pairs with the smp_cond_load_acquire() in try_to_wake_up().
         */
        smp_store_release(&prev->on_cpu, 0);
#endif
}

static inline void
prepare_lock_switch(struct rq *rq, struct task_struct *next, struct rq_flags *rf)
{
        /*
         * Since the runqueue lock will be released by the next
         * task (which is an invalid locking op but in the case
         * of the scheduler it's an obvious special-case), so we
         * do an early lockdep release here:
         */
        rq_unpin_lock(rq, rf);
        spin_release(&rq->lock.dep_map, _THIS_IP_);
#ifdef CONFIG_DEBUG_SPINLOCK
        /* this is a valid case when another task releases the spinlock */
        rq->lock.owner = next;
#endif
}

static inline void finish_lock_switch(struct rq *rq)
{
        /*
         * If we are tracking spinlock dependencies then we have to
         * fix up the runqueue lock - which gets 'carried over' from
         * prev into current:
         */
        spin_acquire(&rq->lock.dep_map, 0, 0, _THIS_IP_);
        raw_spin_unlock_irq(&rq->lock);
}

/*
 * NOP if the arch has not defined these:
 */

#ifndef prepare_arch_switch
# define prepare_arch_switch(next)      do { } while (0)
#endif

#ifndef finish_arch_post_lock_switch
# define finish_arch_post_lock_switch() do { } while (0)
#endif

/**
 * prepare_task_switch - prepare to switch tasks
 * @rq: the runqueue preparing to switch
 * @prev: the current task that is being switched out
 * @next: the task we are going to switch to.
 *
 * This is called with the rq lock held and interrupts off. It must
 * be paired with a subsequent finish_task_switch after the context
 * switch.
 *
 * prepare_task_switch sets up locking and calls architecture specific
 * hooks.
 */
static inline void
prepare_task_switch(struct rq *rq, struct task_struct *prev,
                    struct task_struct *next)
{
        kcov_prepare_switch(prev);
        sched_info_switch(rq, prev, next);
        perf_event_task_sched_out(prev, next);
        rseq_preempt(prev);
        fire_sched_out_preempt_notifiers(prev, next);
        prepare_task(next);
        prepare_arch_switch(next);
}

/**
 * finish_task_switch - clean up after a task-switch
 * @prev: the thread we just switched away from.
 *
 * finish_task_switch must be called after the context switch, paired
 * with a prepare_task_switch call before the context switch.
 * finish_task_switch will reconcile locking set up by prepare_task_switch,
 * and do any other architecture-specific cleanup actions.
 *
 * Note that we may have delayed dropping an mm in context_switch(). If
 * so, we finish that here outside of the runqueue lock. (Doing it
 * with the lock held can cause deadlocks; see schedule() for
 * details.)
 *
 * The context switch have flipped the stack from under us and restored the
 * local variables which were saved when this task called schedule() in the
 * past. prev == current is still correct but we need to recalculate this_rq
 * because prev may have moved to another CPU.
 */
static struct rq *finish_task_switch(struct task_struct *prev)
        __releases(rq->lock)
{
        struct rq *rq = this_rq();
        struct mm_struct *mm = rq->prev_mm;
        long prev_state;

        /*
         * The previous task will have left us with a preempt_count of 2
         * because it left us after:
         *
         *      schedule()
         *        preempt_disable();                    // 1
         *        __schedule()
         *          raw_spin_lock_irq(&rq->lock)        // 2
         *
         * Also, see FORK_PREEMPT_COUNT.
         */
        if (WARN_ONCE(preempt_count() != 2*PREEMPT_DISABLE_OFFSET,
                      "corrupted preempt_count: %s/%d/0x%x\n",
                      current->comm, current->pid, preempt_count()))
                preempt_count_set(FORK_PREEMPT_COUNT);

        rq->prev_mm = NULL;

        /*
         * A task struct has one reference for the use as "current".
         * If a task dies, then it sets TASK_DEAD in tsk->state and calls
         * schedule one last time. The schedule call will never return, and
         * the scheduled task must drop that reference.
         *
         * We must observe prev->state before clearing prev->on_cpu (in
         * finish_task), otherwise a concurrent wakeup can get prev
         * running on another CPU and we could rave with its RUNNING -> DEAD
         * transition, resulting in a double drop.
         */
        prev_state = prev->state;
        vtime_task_switch(prev);
        perf_event_task_sched_in(prev, current);
        finish_task(prev);
        finish_lock_switch(rq);
        finish_arch_post_lock_switch();
        kcov_finish_switch(current);

        fire_sched_in_preempt_notifiers(current);
        /*
         * When switching through a kernel thread, the loop in
         * membarrier_{private,global}_expedited() may have observed that
         * kernel thread and not issued an IPI. It is therefore possible to
         * schedule between user->kernel->user threads without passing though
         * switch_mm(). Membarrier requires a barrier after storing to
         * rq->curr, before returning to userspace, so provide them here:
         *
         * - a full memory barrier for {PRIVATE,GLOBAL}_EXPEDITED, implicitly
         *   provided by mmdrop(),
         * - a sync_core for SYNC_CORE.
         */
        if (mm) {
                membarrier_mm_sync_core_before_usermode(mm);
                mmdrop(mm);
        }
        if (unlikely(prev_state == TASK_DEAD)) {
                if (prev->sched_class->task_dead)
                        prev->sched_class->task_dead(prev);

                /*
                 * Remove function-return probe instances associated with this
                 * task and put them back on the free list.
                 */
                kprobe_flush_task(prev);

                /* Task is done with its stack. */
                put_task_stack(prev);

                put_task_struct_rcu_user(prev);
        }

        tick_nohz_task_switch();
        return rq;
}

#ifdef CONFIG_SMP

/* rq->lock is NOT held, but preemption is disabled */
static void __balance_callback(struct rq *rq)
{
        struct callback_head *head, *next;
        void (*func)(struct rq *rq);
        unsigned long flags;

        raw_spin_lock_irqsave(&rq->lock, flags);
        head = rq->balance_callback;
        rq->balance_callback = NULL;
        while (head) {
                func = (void (*)(struct rq *))head->func;
                next = head->next;
                head->next = NULL;
                head = next;

                func(rq);
        }
        raw_spin_unlock_irqrestore(&rq->lock, flags);
}

static inline void balance_callback(struct rq *rq)
{
        if (unlikely(rq->balance_callback))
                __balance_callback(rq);
}

#else

static inline void balance_callback(struct rq *rq)
{
}

#endif

/**
 * schedule_tail - first thing a freshly forked thread must call.
 * @prev: the thread we just switched away from.
 */
asmlinkage __visible void schedule_tail(struct task_struct *prev)
        __releases(rq->lock)
{
        struct rq *rq;

        /*
         * New tasks start with FORK_PREEMPT_COUNT, see there and
         * finish_task_switch() for details.
         *
         * finish_task_switch() will drop rq->lock() and lower preempt_count
         * and the preempt_enable() will end up enabling preemption (on
         * PREEMPT_COUNT kernels).
         */

        rq = finish_task_switch(prev);
        balance_callback(rq);
        preempt_enable();

        if (current->set_child_tid)
                put_user(task_pid_vnr(current), current->set_child_tid);

        calculate_sigpending();
}

/*
 * context_switch - switch to the new MM and the new thread's register state.
 */
static __always_inline struct rq *
context_switch(struct rq *rq, struct task_struct *prev,
               struct task_struct *next, struct rq_flags *rf)
{
        prepare_task_switch(rq, prev, next);

        /*
         * For paravirt, this is coupled with an exit in switch_to to
         * combine the page table reload and the switch backend into
         * one hypercall.
         */
        arch_start_context_switch(prev);

        /*
         * kernel -> kernel   lazy + transfer active
         *   user -> kernel   lazy + mmgrab() active
         *
         * kernel ->   user   switch + mmdrop() active
         *   user ->   user   switch
         */
        if (!next->mm) {                                // to kernel
                enter_lazy_tlb(prev->active_mm, next);

                next->active_mm = prev->active_mm;
                if (prev->mm)                           // from user
                        mmgrab(prev->active_mm);
                else
                        prev->active_mm = NULL;
        } else {                                        // to user
                membarrier_switch_mm(rq, prev->active_mm, next->mm);
                /*
                 * sys_membarrier() requires an smp_mb() between setting
                 * rq->curr / membarrier_switch_mm() and returning to userspace.
                 *
                 * The below provides this either through switch_mm(), or in
                 * case 'prev->active_mm == next->mm' through
                 * finish_task_switch()'s mmdrop().
                 */
                switch_mm_irqs_off(prev->active_mm, next->mm, next);

                if (!prev->mm) {                        // from kernel
                        /* will mmdrop() in finish_task_switch(). */
                        rq->prev_mm = prev->active_mm;
                        prev->active_mm = NULL;
                }
        }

        rq->clock_update_flags &= ~(RQCF_ACT_SKIP|RQCF_REQ_SKIP);

        prepare_lock_switch(rq, next, rf);

        /* Here we just switch the register state and the stack. */
        switch_to(prev, next, prev);
        barrier();

        return finish_task_switch(prev);
}

/*
 * nr_running and nr_context_switches:
 *
 * externally visible scheduler statistics: current number of runnable
 * threads, total number of context switches performed since bootup.
 */
unsigned long nr_running(void)
{
        unsigned long i, sum = 0;

        for_each_online_cpu(i)
                sum += cpu_rq(i)->nr_running;

        return sum;
}

/*
 * Check if only the current task is running on the CPU.
 *
 * Caution: this function does not check that the caller has disabled
 * preemption, thus the result might have a time-of-check-to-time-of-use
 * race.  The caller is responsible to use it correctly, for example:
 *
 * - from a non-preemptible section (of course)
 *
 * - from a thread that is bound to a single CPU
 *
 * - in a loop with very short iterations (e.g. a polling loop)
 */
bool single_task_running(void)
{
        return raw_rq()->nr_running == 1;
}
EXPORT_SYMBOL(single_task_running);

unsigned long long nr_context_switches(void)
{
        int i;
        unsigned long long sum = 0;

        for_each_possible_cpu(i)
                sum += cpu_rq(i)->nr_switches;

        return sum;
}

/*
 * Consumers of these two interfaces, like for example the cpuidle menu
 * governor, are using nonsensical data. Preferring shallow idle state selection
 * for a CPU that has IO-wait which might not even end up running the task when
 * it does become runnable.
 */

unsigned long nr_iowait_cpu(int cpu)
{
        return atomic_read(&cpu_rq(cpu)->nr_iowait);
}

/*
 * IO-wait accounting, and how its mostly bollocks (on SMP).
 *
 * The idea behind IO-wait account is to account the idle time that we could
 * have spend running if it were not for IO. That is, if we were to improve the
 * storage performance, we'd have a proportional reduction in IO-wait time.
 *
 * This all works nicely on UP, where, when a task blocks on IO, we account
 * idle time as IO-wait, because if the storage were faster, it could've been
 * running and we'd not be idle.
 *
 * This has been extended to SMP, by doing the same for each CPU. This however
 * is broken.
 *
 * Imagine for instance the case where two tasks block on one CPU, only the one
 * CPU will have IO-wait accounted, while the other has regular idle. Even
 * though, if the storage were faster, both could've ran at the same time,
 * utilising both CPUs.
 *
 * This means, that when looking globally, the current IO-wait accounting on
 * SMP is a lower bound, by reason of under accounting.
 *
 * Worse, since the numbers are provided per CPU, they are sometimes
 * interpreted per CPU, and that is nonsensical. A blocked task isn't strictly
 * associated with any one particular CPU, it can wake to another CPU than it
 * blocked on. This means the per CPU IO-wait number is meaningless.
 *
 * Task CPU affinities can make all that even more 'interesting'.
 */

unsigned long nr_iowait(void)
{
        unsigned long i, sum = 0;

        for_each_possible_cpu(i)
                sum += nr_iowait_cpu(i);

        return sum;
}

#ifdef CONFIG_SMP

/*
 * sched_exec - execve() is a valuable balancing opportunity, because at
 * this point the task has the smallest effective memory and cache footprint.
 */
void sched_exec(void)
{
        struct task_struct *p = current;
        unsigned long flags;
        int dest_cpu;

        raw_spin_lock_irqsave(&p->pi_lock, flags);
        dest_cpu = p->sched_class->select_task_rq(p, task_cpu(p), SD_BALANCE_EXEC, 0);
        if (dest_cpu == smp_processor_id())
                goto unlock;

        if (likely(cpu_active(dest_cpu))) {
                struct migration_arg arg = { p, dest_cpu };

                raw_spin_unlock_irqrestore(&p->pi_lock, flags);
                stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg);
                return;
        }
unlock:
        raw_spin_unlock_irqrestore(&p->pi_lock, flags);
}

#endif

DEFINE_PER_CPU(struct kernel_stat, kstat);
DEFINE_PER_CPU(struct kernel_cpustat, kernel_cpustat);

EXPORT_PER_CPU_SYMBOL(kstat);
EXPORT_PER_CPU_SYMBOL(kernel_cpustat);

/*
 * The function fair_sched_class.update_curr accesses the struct curr
 * and its field curr->exec_start; when called from task_sched_runtime(),
 * we observe a high rate of cache misses in practice.
 * Prefetching this data results in improved performance.
 */
static inline void prefetch_curr_exec_start(struct task_struct *p)
{
#ifdef CONFIG_FAIR_GROUP_SCHED
        struct sched_entity *curr = (&p->se)->cfs_rq->curr;
#else
        struct sched_entity *curr = (&task_rq(p)->cfs)->curr;
#endif
        prefetch(curr);
        prefetch(&curr->exec_start);
}

/*
 * Return accounted runtime for the task.
 * In case the task is currently running, return the runtime plus current's
 * pending runtime that have not been accounted yet.
 */
unsigned long long task_sched_runtime(struct task_struct *p)
{
        struct rq_flags rf;
        struct rq *rq;
        u64 ns;

#if defined(CONFIG_64BIT) && defined(CONFIG_SMP)
        /*
         * 64-bit doesn't need locks to atomically read a 64-bit value.
         * So we have a optimization chance when the task's delta_exec is 0.
         * Reading ->on_cpu is racy, but this is ok.
         *
         * If we race with it leaving CPU, we'll take a lock. So we're correct.
         * If we race with it entering CPU, unaccounted time is 0. This is
         * indistinguishable from the read occurring a few cycles earlier.
         * If we see ->on_cpu without ->on_rq, the task is leaving, and has
         * been accounted, so we're correct here as well.
         */
        if (!p->on_cpu || !task_on_rq_queued(p))
                return p->se.sum_exec_runtime;
#endif

        rq = task_rq_lock(p, &rf);
        /*
         * Must be ->curr _and_ ->on_rq.  If dequeued, we would
         * project cycles that may never be accounted to this
         * thread, breaking clock_gettime().
         */
        if (task_current(rq, p) && task_on_rq_queued(p)) {
                prefetch_curr_exec_start(p);
                update_rq_clock(rq);
                p->sched_class->update_curr(rq);
        }
        ns = p->se.sum_exec_runtime;
        task_rq_unlock(rq, p, &rf);

        return ns;
}

DEFINE_PER_CPU(unsigned long, thermal_pressure);

void arch_set_thermal_pressure(struct cpumask *cpus,
                               unsigned long th_pressure)
{
        int cpu;

        for_each_cpu(cpu, cpus)
                WRITE_ONCE(per_cpu(thermal_pressure, cpu), th_pressure);
}

/*
 * This function gets called by the timer code, with HZ frequency.
 * We call it with interrupts disabled.
 */
void scheduler_tick(void)
{
        int cpu = smp_processor_id();
        struct rq *rq = cpu_rq(cpu);
        struct task_struct *curr = rq->curr;
        struct rq_flags rf;
        unsigned long thermal_pressure;

        arch_scale_freq_tick();
        sched_clock_tick();

        rq_lock(rq, &rf);

        update_rq_clock(rq);
        thermal_pressure = arch_scale_thermal_pressure(cpu_of(rq));
        update_thermal_load_avg(rq_clock_thermal(rq), rq, thermal_pressure);
        curr->sched_class->task_tick(rq, curr, 0);
        calc_global_load_tick(rq);
        psi_task_tick(rq);

        rq_unlock(rq, &rf);

        perf_event_task_tick();

#ifdef CONFIG_SMP
        rq->idle_balance = idle_cpu(cpu);
        trigger_load_balance(rq);
#endif
}

#ifdef CONFIG_NO_HZ_FULL

struct tick_work {
        int                     cpu;
        atomic_t                state;
        struct delayed_work     work;
};
/* Values for ->state, see diagram below. */
#define TICK_SCHED_REMOTE_OFFLINE       0
#define TICK_SCHED_REMOTE_OFFLINING     1
#define TICK_SCHED_REMOTE_RUNNING       2

/*
 * State diagram for ->state:
 *
 *
 *          TICK_SCHED_REMOTE_OFFLINE
 *                    |   ^
 *                    |   |
 *                    |   | sched_tick_remote()
 *                    |   |
 *                    |   |
 *                    +--TICK_SCHED_REMOTE_OFFLINING
 *                    |   ^
 *                    |   |
 * sched_tick_start() |   | sched_tick_stop()
 *                    |   |
 *                    V   |
 *          TICK_SCHED_REMOTE_RUNNING
 *
 *
 * Other transitions get WARN_ON_ONCE(), except that sched_tick_remote()
 * and sched_tick_start() are happy to leave the state in RUNNING.
 */

static struct tick_work __percpu *tick_work_cpu;

static void sched_tick_remote(struct work_struct *work)
{
        struct delayed_work *dwork = to_delayed_work(work);
        struct tick_work *twork = container_of(dwork, struct tick_work, work);
        int cpu = twork->cpu;
        struct rq *rq = cpu_rq(cpu);
        struct task_struct *curr;
        struct rq_flags rf;
        u64 delta;
        int os;

        /*
         * Handle the tick only if it appears the remote CPU is running in full
         * dynticks mode. The check is racy by nature, but missing a tick or
         * having one too much is no big deal because the scheduler tick updates
         * statistics and checks timeslices in a time-independent way, regardless
         * of when exactly it is running.
         */
        if (!tick_nohz_tick_stopped_cpu(cpu))
                goto out_requeue;

        rq_lock_irq(rq, &rf);
        curr = rq->curr;
        if (cpu_is_offline(cpu))
                goto out_unlock;

        update_rq_clock(rq);

        if (!is_idle_task(curr)) {
                /*
                 * Make sure the next tick runs within a reasonable
                 * amount of time.
                 */
                delta = rq_clock_task(rq) - curr->se.exec_start;
                WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3);
        }
        curr->sched_class->task_tick(rq, curr, 0);

        calc_load_nohz_remote(rq);
out_unlock:
        rq_unlock_irq(rq, &rf);
out_requeue:

        /*
         * Run the remote tick once per second (1Hz). This arbitrary
         * frequency is large enough to avoid overload but short enough
         * to keep scheduler internal stats reasonably up to date.  But
         * first update state to reflect hotplug activity if required.
         */
        os = atomic_fetch_add_unless(&twork->state, -1, TICK_SCHED_REMOTE_RUNNING);
        WARN_ON_ONCE(os == TICK_SCHED_REMOTE_OFFLINE);
        if (os == TICK_SCHED_REMOTE_RUNNING)
                queue_delayed_work(system_unbound_wq, dwork, HZ);
}

static void sched_tick_start(int cpu)
{
        int os;
        struct tick_work *twork;

        if (housekeeping_cpu(cpu, HK_FLAG_TICK))
                return;

        WARN_ON_ONCE(!tick_work_cpu);

        twork = per_cpu_ptr(tick_work_cpu, cpu);
        os = atomic_xchg(&twork->state, TICK_SCHED_REMOTE_RUNNING);
        WARN_ON_ONCE(os == TICK_SCHED_REMOTE_RUNNING);
        if (os == TICK_SCHED_REMOTE_OFFLINE) {
                twork->cpu = cpu;
                INIT_DELAYED_WORK(&twork->work, sched_tick_remote);
                queue_delayed_work(system_unbound_wq, &twork->work, HZ);
        }
}

#ifdef CONFIG_HOTPLUG_CPU
static void sched_tick_stop(int cpu)
{
        struct tick_work *twork;
        int os;

        if (housekeeping_cpu(cpu, HK_FLAG_TICK))
                return;

        WARN_ON_ONCE(!tick_work_cpu);

        twork = per_cpu_ptr(tick_work_cpu, cpu);
        /* There cannot be competing actions, but don't rely on stop-machine. */
        os = atomic_xchg(&twork->state, TICK_SCHED_REMOTE_OFFLINING);
        WARN_ON_ONCE(os != TICK_SCHED_REMOTE_RUNNING);
        /* Don't cancel, as this would mess up the state machine. */
}
#endif /* CONFIG_HOTPLUG_CPU */

int __init sched_tick_offload_init(void)
{
        tick_work_cpu = alloc_percpu(struct tick_work);
        BUG_ON(!tick_work_cpu);
        return 0;
}

#else /* !CONFIG_NO_HZ_FULL */
static inline void sched_tick_start(int cpu) { }
static inline void sched_tick_stop(int cpu) { }
#endif

#if defined(CONFIG_PREEMPTION) && (defined(CONFIG_DEBUG_PREEMPT) || \
                                defined(CONFIG_TRACE_PREEMPT_TOGGLE))
/*
 * If the value passed in is equal to the current preempt count
 * then we just disabled preemption. Start timing the latency.
 */
static inline void preempt_latency_start(int val)
{
        if (preempt_count() == val) {
                unsigned long ip = get_lock_parent_ip();
#ifdef CONFIG_DEBUG_PREEMPT
                current->preempt_disable_ip = ip;
#endif
                trace_preempt_off(CALLER_ADDR0, ip);
        }
}

void preempt_count_add(int val)
{
#ifdef CONFIG_DEBUG_PREEMPT
        /*
         * Underflow?
         */
        if (DEBUG_LOCKS_WARN_ON((preempt_count() < 0)))
                return;
#endif
        __preempt_count_add(val);
#ifdef CONFIG_DEBUG_PREEMPT
        /*
         * Spinlock count overflowing soon?
         */
        DEBUG_LOCKS_WARN_ON((preempt_count() & PREEMPT_MASK) >=
                                PREEMPT_MASK - 10);
#endif
        preempt_latency_start(val);
}
EXPORT_SYMBOL(preempt_count_add);
NOKPROBE_SYMBOL(preempt_count_add);

/*
 * If the value passed in equals to the current preempt count
 * then we just enabled preemption. Stop timing the latency.
 */
static inline void preempt_latency_stop(int val)
{
        if (preempt_count() == val)
                trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
}

void preempt_count_sub(int val)
{
#ifdef CONFIG_DEBUG_PREEMPT
        /*
         * Underflow?
         */
        if (DEBUG_LOCKS_WARN_ON(val > preempt_count()))
                return;
        /*
         * Is the spinlock portion underflowing?
         */
        if (DEBUG_LOCKS_WARN_ON((val < PREEMPT_MASK) &&
                        !(preempt_count() & PREEMPT_MASK)))
                return;
#endif

        preempt_latency_stop(val);
        __preempt_count_sub(val);
}
EXPORT_SYMBOL(preempt_count_sub);
NOKPROBE_SYMBOL(preempt_count_sub);

#else
static inline void preempt_latency_start(int val) { }
static inline void preempt_latency_stop(int val) { }
#endif

static inline unsigned long get_preempt_disable_ip(struct task_struct *p)
{
#ifdef CONFIG_DEBUG_PREEMPT
        return p->preempt_disable_ip;
#else
        return 0;
#endif
}

/*
 * Print scheduling while atomic bug:
 */
static noinline void __schedule_bug(struct task_struct *prev)
{
        /* Save this before calling printk(), since that will clobber it */
        unsigned long preempt_disable_ip = get_preempt_disable_ip(current);

        if (oops_in_progress)
                return;

        printk(KERN_ERR "BUG: scheduling while atomic: %s/%d/0x%08x\n",
                prev->comm, prev->pid, preempt_count());

        debug_show_held_locks(prev);
        print_modules();
        if (irqs_disabled())
                print_irqtrace_events(prev);
        if (IS_ENABLED(CONFIG_DEBUG_PREEMPT)
            && in_atomic_preempt_off()) {
                pr_err("Preemption disabled at:");
                print_ip_sym(preempt_disable_ip);
                pr_cont("\n");
        }
        if (panic_on_warn)
                panic("scheduling while atomic\n");

        dump_stack();
        add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
}

/*
 * Various schedule()-time debugging checks and statistics:
 */
static inline void schedule_debug(struct task_struct *prev, bool preempt)
{
#ifdef CONFIG_SCHED_STACK_END_CHECK
        if (task_stack_end_corrupted(prev))
                panic("corrupted stack end detected inside scheduler\n");
#endif

#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
        if (!preempt && prev->state && prev->non_block_count) {
                printk(KERN_ERR "BUG: scheduling in a non-blocking section: %s/%d/%i\n",
                        prev->comm, prev->pid, prev->non_block_count);
                dump_stack();
                add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
        }
#endif

        if (unlikely(in_atomic_preempt_off())) {
                __schedule_bug(prev);
                preempt_count_set(PREEMPT_DISABLED);
        }
        rcu_sleep_check();

        profile_hit(SCHED_PROFILING, __builtin_return_address(0));

        schedstat_inc(this_rq()->sched_count);
}

static void put_prev_task_balance(struct rq *rq, struct task_struct *prev,
                                  struct rq_flags *rf)
{
#ifdef CONFIG_SMP
        const struct sched_class *class;
        /*
         * We must do the balancing pass before put_prev_task(), such
         * that when we release the rq->lock the task is in the same
         * state as before we took rq->lock.
         *
         * We can terminate the balance pass as soon as we know there is
         * a runnable task of @class priority or higher.
         */
        for_class_range(class, prev->sched_class, &idle_sched_class) {
                if (class->balance(rq, prev, rf))
                        break;
        }
#endif

        put_prev_task(rq, prev);
}

/*
 * Pick up the highest-prio task:
 */
static inline struct task_struct *
pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
{
        const struct sched_class *class;
        struct task_struct *p;

        /*
         * Optimization: we know that if all tasks are in the fair class we can
         * call that function directly, but only if the @prev task wasn't of a
         * higher scheduling class, because otherwise those loose the
         * opportunity to pull in more work from other CPUs.
         */
        if (likely((prev->sched_class == &idle_sched_class ||
                    prev->sched_class == &fair_sched_class) &&
                   rq->nr_running == rq->cfs.h_nr_running)) {

                p = pick_next_task_fair(rq, prev, rf);
                if (unlikely(p == RETRY_TASK))
                        goto restart;

                /* Assumes fair_sched_class->next == idle_sched_class */
                if (!p) {
                        put_prev_task(rq, prev);
                        p = pick_next_task_idle(rq);
                }

                return p;
        }

restart:
        put_prev_task_balance(rq, prev, rf);

        for_each_class(class) {
                p = class->pick_next_task(rq);
                if (p)
                        return p;
        }

        /* The idle class should always have a runnable task: */
        BUG();
}

/*
 * __schedule() is the main scheduler function.
 *
 * The main means of driving the scheduler and thus entering this function are:
 *
 *   1. Explicit blocking: mutex, semaphore, waitqueue, etc.
 *
 *   2. TIF_NEED_RESCHED flag is checked on interrupt and userspace return
 *      paths. For example, see arch/x86/entry_64.S.
 *
 *      To drive preemption between tasks, the scheduler sets the flag in timer
 *      interrupt handler scheduler_tick().
 *
 *   3. Wakeups don't really cause entry into schedule(). They add a
 *      task to the run-queue and that's it.
 *
 *      Now, if the new task added to the run-queue preempts the current
 *      task, then the wakeup sets TIF_NEED_RESCHED and schedule() gets
 *      called on the nearest possible occasion:
 *
 *       - If the kernel is preemptible (CONFIG_PREEMPTION=y):
 *
 *         - in syscall or exception context, at the next outmost
 *           preempt_enable(). (this might be as soon as the wake_up()'s
 *           spin_unlock()!)
 *
 *         - in IRQ context, return from interrupt-handler to
 *           preemptible context
 *
 *       - If the kernel is not preemptible (CONFIG_PREEMPTION is not set)
 *         then at the next:
 *
 *          - cond_resched() call
 *          - explicit schedule() call
 *          - return from syscall or exception to user-space
 *          - return from interrupt-handler to user-space
 *
 * WARNING: must be called with preemption disabled!
 */
static void __sched notrace __schedule(bool preempt)
{
        struct task_struct *prev, *next;
        unsigned long *switch_count;
        struct rq_flags rf;
        struct rq *rq;
        int cpu;

        cpu = smp_processor_id();
        rq = cpu_rq(cpu);
        prev = rq->curr;

        schedule_debug(prev, preempt);

        if (sched_feat(HRTICK))
                hrtick_clear(rq);

        local_irq_disable();
        rcu_note_context_switch(preempt);

        /*
         * Make sure that signal_pending_state()->signal_pending() below
         * can't be reordered with __set_current_state(TASK_INTERRUPTIBLE)
         * done by the caller to avoid the race with signal_wake_up().
         *
         * The membarrier system call requires a full memory barrier
         * after coming from user-space, before storing to rq->curr.
         */
        rq_lock(rq, &rf);
        smp_mb__after_spinlock();

        /* Promote REQ to ACT */
        rq->clock_update_flags <<= 1;
        update_rq_clock(rq);

        switch_count = &prev->nivcsw;
        if (!preempt && prev->state) {
                if (signal_pending_state(prev->state, prev)) {
                        prev->state = TASK_RUNNING;
                } else {
                        deactivate_task(rq, prev, DEQUEUE_SLEEP | DEQUEUE_NOCLOCK);

                        if (prev->in_iowait) {
                                atomic_inc(&rq->nr_iowait);
                                delayacct_blkio_start();
                        }
                }
                switch_count = &prev->nvcsw;
        }

        next = pick_next_task(rq, prev, &rf);
        clear_tsk_need_resched(prev);
        clear_preempt_need_resched();

        if (likely(prev != next)) {
                rq->nr_switches++;
                /*
                 * RCU users of rcu_dereference(rq->curr) may not see
                 * changes to task_struct made by pick_next_task().
                 */
                RCU_INIT_POINTER(rq->curr, next);
                /*
                 * The membarrier system call requires each architecture
                 * to have a full memory barrier after updating
                 * rq->curr, before returning to user-space.
                 *
                 * Here are the schemes providing that barrier on the
                 * various architectures:
                 * - mm ? switch_mm() : mmdrop() for x86, s390, sparc, PowerPC.
                 *   switch_mm() rely on membarrier_arch_switch_mm() on PowerPC.
                 * - finish_lock_switch() for weakly-ordered
                 *   architectures where spin_unlock is a full barrier,
                 * - switch_to() for arm64 (weakly-ordered, spin_unlock
                 *   is a RELEASE barrier),
                 */
                ++*switch_count;

                psi_sched_switch(prev, next, !task_on_rq_queued(prev));

                trace_sched_switch(preempt, prev, next);

                /* Also unlocks the rq: */
                rq = context_switch(rq, prev, next, &rf);
        } else {
                rq->clock_update_flags &= ~(RQCF_ACT_SKIP|RQCF_REQ_SKIP);
                rq_unlock_irq(rq, &rf);
        }

        balance_callback(rq);
}

void __noreturn do_task_dead(void)
{
        /* Causes final put_task_struct in finish_task_switch(): */
        set_special_state(TASK_DEAD);

        /* Tell freezer to ignore us: */
        current->flags |= PF_NOFREEZE;

        __schedule(false);
        BUG();

        /* Avoid "noreturn function does return" - but don't continue if BUG() is a NOP: */
        for (;;)
                cpu_relax();
}

static inline void sched_submit_work(struct task_struct *tsk)
{
        if (!tsk->state)
                return;

        /*
         * If a worker went to sleep, notify and ask workqueue whether
         * it wants to wake up a task to maintain concurrency.
         * As this function is called inside the schedule() context,
         * we disable preemption to avoid it calling schedule() again
         * in the possible wakeup of a kworker and because wq_worker_sleeping()
         * requires it.
         */
        if (tsk->flags & (PF_WQ_WORKER | PF_IO_WORKER)) {
                preempt_disable();
                if (tsk->flags & PF_WQ_WORKER)
                        wq_worker_sleeping(tsk);
                else
                        io_wq_worker_sleeping(tsk);
                preempt_enable_no_resched();
        }

        if (tsk_is_pi_blocked(tsk))
                return;

        /*
         * If we are going to sleep and we have plugged IO queued,
         * make sure to submit it to avoid deadlocks.
         */
        if (blk_needs_flush_plug(tsk))
                blk_schedule_flush_plug(tsk);
}

static void sched_update_worker(struct task_struct *tsk)
{
        if (tsk->flags & (PF_WQ_WORKER | PF_IO_WORKER)) {
                if (tsk->flags & PF_WQ_WORKER)
                        wq_worker_running(tsk);
                else
                        io_wq_worker_running(tsk);
        }
}

asmlinkage __visible void __sched schedule(void)
{
        struct task_struct *tsk = current;

        sched_submit_work(tsk);
        do {
                preempt_disable();
                __schedule(false);
                sched_preempt_enable_no_resched();
        } while (need_resched());
        sched_update_worker(tsk);
}
EXPORT_SYMBOL(schedule);

/*
 * synchronize_rcu_tasks() makes sure that no task is stuck in preempted
 * state (have scheduled out non-voluntarily) by making sure that all
 * tasks have either left the run queue or have gone into user space.
 * As idle tasks do not do either, they must not ever be preempted
 * (schedule out non-voluntarily).
 *
 * schedule_idle() is similar to schedule_preempt_disable() except that it
 * never enables preemption because it does not call sched_submit_work().
 */
void __sched schedule_idle(void)
{
        /*
         * As this skips calling sched_submit_work(), which the idle task does
         * regardless because that function is a nop when the task is in a
         * TASK_RUNNING state, make sure this isn't used someplace that the
         * current task can be in any other state. Note, idle is always in the
         * TASK_RUNNING state.
         */
        WARN_ON_ONCE(current->state);
        do {
                __schedule(false);
        } while (need_resched());
}

#ifdef CONFIG_CONTEXT_TRACKING
asmlinkage __visible void __sched schedule_user(void)
{
        /*
         * If we come here after a random call to set_need_resched(),
         * or we have been woken up remotely but the IPI has not yet arrived,
         * we haven't yet exited the RCU idle mode. Do it here manually until
         * we find a better solution.
         *
         * NB: There are buggy callers of this function.  Ideally we
         * should warn if prev_state != CONTEXT_USER, but that will trigger
         * too frequently to make sense yet.
         */
        enum ctx_state prev_state = exception_enter();
        schedule();
        exception_exit(prev_state);
}
#endif

/**
 * schedule_preempt_disabled - called with preemption disabled
 *
 * Returns with preemption disabled. Note: preempt_count must be 1
 */
void __sched schedule_preempt_disabled(void)
{
        sched_preempt_enable_no_resched();
        schedule();
        preempt_disable();
}

static void __sched notrace preempt_schedule_common(void)
{
        do {
                /*
                 * Because the function tracer can trace preempt_count_sub()
                 * and it also uses preempt_enable/disable_notrace(), if
                 * NEED_RESCHED is set, the preempt_enable_notrace() called
                 * by the function tracer will call this function again and
                 * cause infinite recursion.
                 *
                 * Preemption must be disabled here before the function
                 * tracer can trace. Break up preempt_disable() into two
                 * calls. One to disable preemption without fear of being
                 * traced. The other to still record the preemption latency,
                 * which can also be traced by the function tracer.
                 */
                preempt_disable_notrace();
                preempt_latency_start(1);
                __schedule(true);
                preempt_latency_stop(1);
                preempt_enable_no_resched_notrace();

                /*
                 * Check again in case we missed a preemption opportunity
                 * between schedule and now.
                 */
        } while (need_resched());
}

#ifdef CONFIG_PREEMPTION
/*
 * This is the entry point to schedule() from in-kernel preemption
 * off of preempt_enable.
 */
asmlinkage __visible void __sched notrace preempt_schedule(void)
{
        /*
         * If there is a non-zero preempt_count or interrupts are disabled,
         * we do not want to preempt the current task. Just return..
         */
        if (likely(!preemptible()))
                return;

        preempt_schedule_common();
}
NOKPROBE_SYMBOL(preempt_schedule);
EXPORT_SYMBOL(preempt_schedule);

/**
 * preempt_schedule_notrace - preempt_schedule called by tracing
 *
 * The tracing infrastructure uses preempt_enable_notrace to prevent
 * recursion and tracing preempt enabling caused by the tracing
 * infrastructure itself. But as tracing can happen in areas coming
 * from userspace or just about to enter userspace, a preempt enable
 * can occur before user_exit() is called. This will cause the scheduler
 * to be called when the system is still in usermode.
 *
 * To prevent this, the preempt_enable_notrace will use this function
 * instead of preempt_schedule() to exit user context if needed before
 * calling the scheduler.
 */
asmlinkage __visible void __sched notrace preempt_schedule_notrace(void)
{
        enum ctx_state prev_ctx;

        if (likely(!preemptible()))
                return;

        do {
                /*
                 * Because the function tracer can trace preempt_count_sub()
                 * and it also uses preempt_enable/disable_notrace(), if
                 * NEED_RESCHED is set, the preempt_enable_notrace() called
                 * by the function tracer will call this function again and
                 * cause infinite recursion.
                 *
                 * Preemption must be disabled here before the function
                 * tracer can trace. Break up preempt_disable() into two
                 * calls. One to disable preemption without fear of being
                 * traced. The other to still record the preemption latency,
                 * which can also be traced by the function tracer.
                 */
                preempt_disable_notrace();
                preempt_latency_start(1);
                /*
                 * Needs preempt disabled in case user_exit() is traced
                 * and the tracer calls preempt_enable_notrace() causing
                 * an infinite recursion.
                 */
                prev_ctx = exception_enter();
                __schedule(true);
                exception_exit(prev_ctx);

                preempt_latency_stop(1);
                preempt_enable_no_resched_notrace();
        } while (need_resched());
}
EXPORT_SYMBOL_GPL(preempt_schedule_notrace);

#endif /* CONFIG_PREEMPTION */

/*
 * This is the entry point to schedule() from kernel preemption
 * off of irq context.
 * Note, that this is called and return with irqs disabled. This will
 * protect us against recursive calling from irq.
 */
asmlinkage __visible void __sched preempt_schedule_irq(void)
{
        enum ctx_state prev_state;

        /* Catch callers which need to be fixed */
        BUG_ON(preempt_count() || !irqs_disabled());

        prev_state = exception_enter();

        do {
                preempt_disable();
                local_irq_enable();
                __schedule(true);
                local_irq_disable();
                sched_preempt_enable_no_resched();
        } while (need_resched());

        exception_exit(prev_state);
}

int default_wake_function(wait_queue_entry_t *curr, unsigned mode, int wake_flags,
                          void *key)
{
        return try_to_wake_up(curr->private, mode, wake_flags);
}
EXPORT_SYMBOL(default_wake_function);

#ifdef CONFIG_RT_MUTEXES

static inline int __rt_effective_prio(struct task_struct *pi_task, int prio)
{
        if (pi_task)
                prio = min(prio, pi_task->prio);

        return prio;
}

static inline int rt_effective_prio(struct task_struct *p, int prio)
{
        struct task_struct *pi_task = rt_mutex_get_top_task(p);

        return __rt_effective_prio(pi_task, prio);
}

/*
 * rt_mutex_setprio - set the current priority of a task
 * @p: task to boost
 * @pi_task: donor task
 *
 * This function changes the 'effective' priority of a task. It does
 * not touch ->normal_prio like __setscheduler().
 *
 * Used by the rt_mutex code to implement priority inheritance
 * logic. Call site only calls if the priority of the task changed.
 */
void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task)
{
        int prio, oldprio, queued, running, queue_flag =
                DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
        const struct sched_class *prev_class;
        struct rq_flags rf;
        struct rq *rq;

        /* XXX used to be waiter->prio, not waiter->task->prio */
        prio = __rt_effective_prio(pi_task, p->normal_prio);

        /*
         * If nothing changed; bail early.
         */
        if (p->pi_top_task == pi_task && prio == p->prio && !dl_prio(prio))
                return;

        rq = __task_rq_lock(p, &rf);
        update_rq_clock(rq);
        /*
         * Set under pi_lock && rq->lock, such that the value can be used under
         * either lock.
         *
         * Note that there is loads of tricky to make this pointer cache work
         * right. rt_mutex_slowunlock()+rt_mutex_postunlock() work together to
         * ensure a task is de-boosted (pi_task is set to NULL) before the
         * task is allowed to run again (and can exit). This ensures the pointer
         * points to a blocked task -- which guaratees the task is present.
         */
        p->pi_top_task = pi_task;

        /*
         * For FIFO/RR we only need to set prio, if that matches we're done.
         */
        if (prio == p->prio && !dl_prio(prio))
                goto out_unlock;

        /*
         * Idle task boosting is a nono in general. There is one
         * exception, when PREEMPT_RT and NOHZ is active:
         *
         * The idle task calls get_next_timer_interrupt() and holds
         * the timer wheel base->lock on the CPU and another CPU wants
         * to access the timer (probably to cancel it). We can safely
         * ignore the boosting request, as the idle CPU runs this code
         * with interrupts disabled and will complete the lock
         * protected section without being interrupted. So there is no
         * real need to boost.
         */
        if (unlikely(p == rq->idle)) {
                WARN_ON(p != rq->curr);
                WARN_ON(p->pi_blocked_on);
                goto out_unlock;
        }

        trace_sched_pi_setprio(p, pi_task);
        oldprio = p->prio;

        if (oldprio == prio)
                queue_flag &= ~DEQUEUE_MOVE;

        prev_class = p->sched_class;
        queued = task_on_rq_queued(p);
        running = task_current(rq, p);
        if (queued)
                dequeue_task(rq, p, queue_flag);
        if (running)
                put_prev_task(rq, p);

        /*
         * Boosting condition are:
         * 1. -rt task is running and holds mutex A
         *      --> -dl task blocks on mutex A
         *
         * 2. -dl task is running and holds mutex A
         *      --> -dl task blocks on mutex A and could preempt the
         *          running task
         */
        if (dl_prio(prio)) {
                if (!dl_prio(p->normal_prio) ||
                    (pi_task && dl_entity_preempt(&pi_task->dl, &p->dl))) {
                        p->dl.dl_boosted = 1;
                        queue_flag |= ENQUEUE_REPLENISH;
                } else
                        p->dl.dl_boosted = 0;
                p->sched_class = &dl_sched_class;
        } else if (rt_prio(prio)) {
                if (dl_prio(oldprio))
                        p->dl.dl_boosted = 0;
                if (oldprio < prio)
                        queue_flag |= ENQUEUE_HEAD;
                p->sched_class = &rt_sched_class;
        } else {
                if (dl_prio(oldprio))
                        p->dl.dl_boosted = 0;
                if (rt_prio(oldprio))
                        p->rt.timeout = 0;
                p->sched_class = &fair_sched_class;
        }

        p->prio = prio;

        if (queued)
                enqueue_task(rq, p, queue_flag);
        if (running)
                set_next_task(rq, p);

        check_class_changed(rq, p, prev_class, oldprio);
out_unlock:
        /* Avoid rq from going away on us: */
        preempt_disable();
        __task_rq_unlock(rq, &rf);

        balance_callback(rq);
        preempt_enable();
}
#else
static inline int rt_effective_prio(struct task_struct *p, int prio)
{
        return prio;
}
#endif

void set_user_nice(struct task_struct *p, long nice)
{
        bool queued, running;
        int old_prio;
        struct rq_flags rf;
        struct rq *rq;

        if (task_nice(p) == nice || nice < MIN_NICE || nice > MAX_NICE)
                return;
        /*
         * We have to be careful, if called from sys_setpriority(),
         * the task might be in the middle of scheduling on another CPU.
         */
        rq = task_rq_lock(p, &rf);
        update_rq_clock(rq);

        /*
         * The RT priorities are set via sched_setscheduler(), but we still
         * allow the 'normal' nice value to be set - but as expected
         * it wont have any effect on scheduling until the task is
         * SCHED_DEADLINE, SCHED_FIFO or SCHED_RR:
         */
        if (task_has_dl_policy(p) || task_has_rt_policy(p)) {
                p->static_prio = NICE_TO_PRIO(nice);
                goto out_unlock;
        }
        queued = task_on_rq_queued(p);
        running = task_current(rq, p);
        if (queued)
                dequeue_task(rq, p, DEQUEUE_SAVE | DEQUEUE_NOCLOCK);
        if (running)
                put_prev_task(rq, p);

        p->static_prio = NICE_TO_PRIO(nice);
        set_load_weight(p, true);
        old_prio = p->prio;
        p->prio = effective_prio(p);

        if (queued)
                enqueue_task(rq, p, ENQUEUE_RESTORE | ENQUEUE_NOCLOCK);
        if (running)
                set_next_task(rq, p);

        /*
         * If the task increased its priority or is running and
         * lowered its priority, then reschedule its CPU:
         */
        p->sched_class->prio_changed(rq, p, old_prio);

out_unlock:
        task_rq_unlock(rq, p, &rf);
}
EXPORT_SYMBOL(set_user_nice);

/*
 * can_nice - check if a task can reduce its nice value
 * @p: task
 * @nice: nice value
 */
int can_nice(const struct task_struct *p, const int nice)
{
        /* Convert nice value [19,-20] to rlimit style value [1,40]: */
        int nice_rlim = nice_to_rlimit(nice);

        return (nice_rlim <= task_rlimit(p, RLIMIT_NICE) ||
                capable(CAP_SYS_NICE));
}

#ifdef __ARCH_WANT_SYS_NICE

/*
 * sys_nice - change the priority of the current process.
 * @increment: priority increment
 *
 * sys_setpriority is a more generic, but much slower function that
 * does similar things.
 */
SYSCALL_DEFINE1(nice, int, increment)
{
        long nice, retval;

        /*
         * Setpriority might change our priority at the same moment.
         * We don't have to worry. Conceptually one call occurs first
         * and we have a single winner.
         */
        increment = clamp(increment, -NICE_WIDTH, NICE_WIDTH);
        nice = task_nice(current) + increment;

        nice = clamp_val(nice, MIN_NICE, MAX_NICE);
        if (increment < 0 && !can_nice(current, nice))
                return -EPERM;

        retval = security_task_setnice(current, nice);
        if (retval)
                return retval;

        set_user_nice(current, nice);
        return 0;
}

#endif

/**
 * task_prio - return the priority value of a given task.
 * @p: the task in question.
 *
 * Return: The priority value as seen by users in /proc.
 * RT tasks are offset by -200. Normal tasks are centered
 * around 0, value goes from -16 to +15.
 */
int task_prio(const struct task_struct *p)
{
        return p->prio - MAX_RT_PRIO;
}

/**
 * idle_cpu - is a given CPU idle currently?
 * @cpu: the processor in question.
 *
 * Return: 1 if the CPU is currently idle. 0 otherwise.
 */
int idle_cpu(int cpu)
{
        struct rq *rq = cpu_rq(cpu);

        if (rq->curr != rq->idle)
                return 0;

        if (rq->nr_running)
                return 0;

#ifdef CONFIG_SMP
        if (!llist_empty(&rq->wake_list))
                return 0;
#endif

        return 1;
}

/**
 * available_idle_cpu - is a given CPU idle for enqueuing work.
 * @cpu: the CPU in question.
 *
 * Return: 1 if the CPU is currently idle. 0 otherwise.
 */
int available_idle_cpu(int cpu)
{
        if (!idle_cpu(cpu))
                return 0;

        if (vcpu_is_preempted(cpu))
                return 0;

        return 1;
}

/**
 * idle_task - return the idle task for a given CPU.
 * @cpu: the processor in question.
 *
 * Return: The idle task for the CPU @cpu.
 */
struct task_struct *idle_task(int cpu)
{
        return cpu_rq(cpu)->idle;
}

/**
 * find_process_by_pid - find a process with a matching PID value.
 * @pid: the pid in question.
 *
 * The task of @pid, if found. %NULL otherwise.
 */
static struct task_struct *find_process_by_pid(pid_t pid)
{
        return pid ? find_task_by_vpid(pid) : current;
}

/*
 * sched_setparam() passes in -1 for its policy, to let the functions
 * it calls know not to change it.
 */
#define SETPARAM_POLICY -1

static void __setscheduler_params(struct task_struct *p,
                const struct sched_attr *attr)
{
        int policy = attr->sched_policy;

        if (policy == SETPARAM_POLICY)
                policy = p->policy;

        p->policy = policy;

        if (dl_policy(policy))
                __setparam_dl(p, attr);
        else if (fair_policy(policy))
                p->static_prio = NICE_TO_PRIO(attr->sched_nice);

        /*
         * __sched_setscheduler() ensures attr->sched_priority == 0 when
         * !rt_policy. Always setting this ensures that things like
         * getparam()/getattr() don't report silly values for !rt tasks.
         */
        p->rt_priority = attr->sched_priority;
        p->normal_prio = normal_prio(p);
        set_load_weight(p, true);
}

/* Actually do priority change: must hold pi & rq lock. */
static void __setscheduler(struct rq *rq, struct task_struct *p,
                           const struct sched_attr *attr, bool keep_boost)
{
        /*
         * If params can't change scheduling class changes aren't allowed
         * either.
         */
        if (attr->sched_flags & SCHED_FLAG_KEEP_PARAMS)
                return;

        __setscheduler_params(p, attr);

        /*
         * Keep a potential priority boosting if called from
         * sched_setscheduler().
         */
        p->prio = normal_prio(p);
        if (keep_boost)
                p->prio = rt_effective_prio(p, p->prio);

        if (dl_prio(p->prio))
                p->sched_class = &dl_sched_class;
        else if (rt_prio(p->prio))
                p->sched_class = &rt_sched_class;
        else
                p->sched_class = &fair_sched_class;
}

/*
 * Check the target process has a UID that matches the current process's:
 */
static bool check_same_owner(struct task_struct *p)
{
        const struct cred *cred = current_cred(), *pcred;
        bool match;

        rcu_read_lock();
        pcred = __task_cred(p);
        match = (uid_eq(cred->euid, pcred->euid) ||
                 uid_eq(cred->euid, pcred->uid));
        rcu_read_unlock();
        return match;
}

static int __sched_setscheduler(struct task_struct *p,
                                const struct sched_attr *attr,
                                bool user, bool pi)
{
        int newprio = dl_policy(attr->sched_policy) ? MAX_DL_PRIO - 1 :
                      MAX_RT_PRIO - 1 - attr->sched_priority;
        int retval, oldprio, oldpolicy = -1, queued, running;
        int new_effective_prio, policy = attr->sched_policy;
        const struct sched_class *prev_class;
        struct rq_flags rf;
        int reset_on_fork;
        int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
        struct rq *rq;

        /* The pi code expects interrupts enabled */
        BUG_ON(pi && in_interrupt());
recheck:
        /* Double check policy once rq lock held: */
        if (policy < 0) {
                reset_on_fork = p->sched_reset_on_fork;
                policy = oldpolicy = p->policy;
        } else {
                reset_on_fork = !!(attr->sched_flags & SCHED_FLAG_RESET_ON_FORK);

                if (!valid_policy(policy))
                        return -EINVAL;
        }

        if (attr->sched_flags & ~(SCHED_FLAG_ALL | SCHED_FLAG_SUGOV))
                return -EINVAL;

        /*
         * Valid priorities for SCHED_FIFO and SCHED_RR are
         * 1..MAX_USER_RT_PRIO-1, valid priority for SCHED_NORMAL,
         * SCHED_BATCH and SCHED_IDLE is 0.
         */
        if ((p->mm && attr->sched_priority > MAX_USER_RT_PRIO-1) ||
            (!p->mm && attr->sched_priority > MAX_RT_PRIO-1))
                return -EINVAL;
        if ((dl_policy(policy) && !__checkparam_dl(attr)) ||
            (rt_policy(policy) != (attr->sched_priority != 0)))
                return -EINVAL;

        /*
         * Allow unprivileged RT tasks to decrease priority:
         */
        if (user && !capable(CAP_SYS_NICE)) {
                if (fair_policy(policy)) {
                        if (attr->sched_nice < task_nice(p) &&
                            !can_nice(p, attr->sched_nice))
                                return -EPERM;
                }

                if (rt_policy(policy)) {
                        unsigned long rlim_rtprio =
                                        task_rlimit(p, RLIMIT_RTPRIO);

                        /* Can't set/change the rt policy: */
                        if (policy != p->policy && !rlim_rtprio)
                                return -EPERM;

                        /* Can't increase priority: */
                        if (attr->sched_priority > p->rt_priority &&
                            attr->sched_priority > rlim_rtprio)
                                return -EPERM;
                }

                 /*
                  * Can't set/change SCHED_DEADLINE policy at all for now
                  * (safest behavior); in the future we would like to allow
                  * unprivileged DL tasks to increase their relative deadline
                  * or reduce their runtime (both ways reducing utilization)
                  */
                if (dl_policy(policy))
                        return -EPERM;

                /*
                 * Treat SCHED_IDLE as nice 20. Only allow a switch to
                 * SCHED_NORMAL if the RLIMIT_NICE would normally permit it.
                 */
                if (task_has_idle_policy(p) && !idle_policy(policy)) {
                        if (!can_nice(p, task_nice(p)))
                                return -EPERM;
                }

                /* Can't change other user's priorities: */
                if (!check_same_owner(p))
                        return -EPERM;

                /* Normal users shall not reset the sched_reset_on_fork flag: */
                if (p->sched_reset_on_fork && !reset_on_fork)
                        return -EPERM;
        }

        if (user) {
                if (attr->sched_flags & SCHED_FLAG_SUGOV)
                        return -EINVAL;

                retval = security_task_setscheduler(p);
                if (retval)
                        return retval;
        }

        /* Update task specific "requested" clamps */
        if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP) {
                retval = uclamp_validate(p, attr);
                if (retval)
                        return retval;
        }

        if (pi)
                cpuset_read_lock();

        /*
         * Make sure no PI-waiters arrive (or leave) while we are
         * changing the priority of the task:
         *
         * To be able to change p->policy safely, the appropriate
         * runqueue lock must be held.
         */
        rq = task_rq_lock(p, &rf);
        update_rq_clock(rq);

        /*
         * Changing the policy of the stop threads its a very bad idea:
         */
        if (p == rq->stop) {
                retval = -EINVAL;
                goto unlock;
        }

        /*
         * If not changing anything there's no need to proceed further,
         * but store a possible modification of reset_on_fork.
         */
        if (unlikely(policy == p->policy)) {
                if (fair_policy(policy) && attr->sched_nice != task_nice(p))
                        goto change;
                if (rt_policy(policy) && attr->sched_priority != p->rt_priority)
                        goto change;
                if (dl_policy(policy) && dl_param_changed(p, attr))
                        goto change;
                if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)
                        goto change;

                p->sched_reset_on_fork = reset_on_fork;
                retval = 0;
                goto unlock;
        }
change:

        if (user) {
#ifdef CONFIG_RT_GROUP_SCHED
                /*
                 * Do not allow realtime tasks into groups that have no runtime
                 * assigned.
                 */
                if (rt_bandwidth_enabled() && rt_policy(policy) &&
                                task_group(p)->rt_bandwidth.rt_runtime == 0 &&
                                !task_group_is_autogroup(task_group(p))) {
                        retval = -EPERM;
                        goto unlock;
                }
#endif
#ifdef CONFIG_SMP
                if (dl_bandwidth_enabled() && dl_policy(policy) &&
                                !(attr->sched_flags & SCHED_FLAG_SUGOV)) {
                        cpumask_t *span = rq->rd->span;

                        /*
                         * Don't allow tasks with an affinity mask smaller than
                         * the entire root_domain to become SCHED_DEADLINE. We
                         * will also fail if there's no bandwidth available.
                         */
                        if (!cpumask_subset(span, p->cpus_ptr) ||
                            rq->rd->dl_bw.bw == 0) {
                                retval = -EPERM;
                                goto unlock;
                        }
                }
#endif
        }

        /* Re-check policy now with rq lock held: */
        if (unlikely(oldpolicy != -1 && oldpolicy != p->policy)) {
                policy = oldpolicy = -1;
                task_rq_unlock(rq, p, &rf);
                if (pi)
                        cpuset_read_unlock();
                goto recheck;
        }

        /*
         * If setscheduling to SCHED_DEADLINE (or changing the parameters
         * of a SCHED_DEADLINE task) we need to check if enough bandwidth
         * is available.
         */
        if ((dl_policy(policy) || dl_task(p)) && sched_dl_overflow(p, policy, attr)) {
                retval = -EBUSY;
                goto unlock;
        }

        p->sched_reset_on_fork = reset_on_fork;
        oldprio = p->prio;

        if (pi) {
                /*
                 * Take priority boosted tasks into account. If the new
                 * effective priority is unchanged, we just store the new
                 * normal parameters and do not touch the scheduler class and
                 * the runqueue. This will be done when the task deboost
                 * itself.
                 */
                new_effective_prio = rt_effective_prio(p, newprio);
                if (new_effective_prio == oldprio)
                        queue_flags &= ~DEQUEUE_MOVE;
        }

        queued = task_on_rq_queued(p);
        running = task_current(rq, p);
        if (queued)
                dequeue_task(rq, p, queue_flags);
        if (running)
                put_prev_task(rq, p);

        prev_class = p->sched_class;

        __setscheduler(rq, p, attr, pi);
        __setscheduler_uclamp(p, attr);

        if (queued) {
                /*
                 * We enqueue to tail when the priority of a task is
                 * increased (user space view).
                 */
                if (oldprio < p->prio)
                        queue_flags |= ENQUEUE_HEAD;

                enqueue_task(rq, p, queue_flags);
        }
        if (running)
                set_next_task(rq, p);

        check_class_changed(rq, p, prev_class, oldprio);

        /* Avoid rq from going away on us: */
        preempt_disable();
        task_rq_unlock(rq, p, &rf);

        if (pi) {
                cpuset_read_unlock();
                rt_mutex_adjust_pi(p);
        }

        /* Run balance callbacks after we've adjusted the PI chain: */
        balance_callback(rq);
        preempt_enable();

        return 0;

unlock:
        task_rq_unlock(rq, p, &rf);
        if (pi)
                cpuset_read_unlock();
        return retval;
}

static int _sched_setscheduler(struct task_struct *p, int policy,
                               const struct sched_param *param, bool check)
{
        struct sched_attr attr = {
                .sched_policy   = policy,
                .sched_priority = param->sched_priority,
                .sched_nice     = PRIO_TO_NICE(p->static_prio),
        };

        /* Fixup the legacy SCHED_RESET_ON_FORK hack. */
        if ((policy != SETPARAM_POLICY) && (policy & SCHED_RESET_ON_FORK)) {
                attr.sched_flags |= SCHED_FLAG_RESET_ON_FORK;
                policy &= ~SCHED_RESET_ON_FORK;
                attr.sched_policy = policy;
        }

        return __sched_setscheduler(p, &attr, check, true);
}
/**
 * sched_setscheduler - change the scheduling policy and/or RT priority of a thread.
 * @p: the task in question.
 * @policy: new policy.
 * @param: structure containing the new RT priority.
 *
 * Return: 0 on success. An error code otherwise.
 *
 * NOTE that the task may be already dead.
 */
int sched_setscheduler(struct task_struct *p, int policy,
                       const struct sched_param *param)
{
        return _sched_setscheduler(p, policy, param, true);
}
EXPORT_SYMBOL_GPL(sched_setscheduler);

int sched_setattr(struct task_struct *p, const struct sched_attr *attr)
{
        return __sched_setscheduler(p, attr, true, true);
}
EXPORT_SYMBOL_GPL(sched_setattr);

int sched_setattr_nocheck(struct task_struct *p, const struct sched_attr *attr)
{
        return __sched_setscheduler(p, attr, false, true);
}

/**
 * sched_setscheduler_nocheck - change the scheduling policy and/or RT priority of a thread from kernelspace.
 * @p: the task in question.
 * @policy: new policy.
 * @param: structure containing the new RT priority.
 *
 * Just like sched_setscheduler, only don't bother checking if the
 * current context has permission.  For example, this is needed in
 * stop_machine(): we create temporary high priority worker threads,
 * but our caller might not have that capability.
 *
 * Return: 0 on success. An error code otherwise.
 */
int sched_setscheduler_nocheck(struct task_struct *p, int policy,
                               const struct sched_param *param)
{
        return _sched_setscheduler(p, policy, param, false);
}
EXPORT_SYMBOL_GPL(sched_setscheduler_nocheck);

static int
do_sched_setscheduler(pid_t pid, int policy, struct sched_param __user *param)
{
        struct sched_param lparam;
        struct task_struct *p;
        int retval;

        if (!param || pid < 0)
                return -EINVAL;
        if (copy_from_user(&lparam, param, sizeof(struct sched_param)))
                return -EFAULT;

        rcu_read_lock();
        retval = -ESRCH;
        p = find_process_by_pid(pid);
        if (likely(p))
                get_task_struct(p);
        rcu_read_unlock();

        if (likely(p)) {
                retval = sched_setscheduler(p, policy, &lparam);
                put_task_struct(p);
        }

        return retval;
}

/*
 * Mimics kernel/events/core.c perf_copy_attr().
 */
static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *attr)
{
        u32 size;
        int ret;

        /* Zero the full structure, so that a short copy will be nice: */
        memset(attr, 0, sizeof(*attr));

        ret = get_user(size, &uattr->size);
        if (ret)
                return ret;

        /* ABI compatibility quirk: */
        if (!size)
                size = SCHED_ATTR_SIZE_VER0;
        if (size < SCHED_ATTR_SIZE_VER0 || size > PAGE_SIZE)
                goto err_size;

        ret = copy_struct_from_user(attr, sizeof(*attr), uattr, size);
        if (ret) {
                if (ret == -E2BIG)
                        goto err_size;
                return ret;
        }

        if ((attr->sched_flags & SCHED_FLAG_UTIL_CLAMP) &&
            size < SCHED_ATTR_SIZE_VER1)
                return -EINVAL;

        /*
         * XXX: Do we want to be lenient like existing syscalls; or do we want
         * to be strict and return an error on out-of-bounds values?
         */
        attr->sched_nice = clamp(attr->sched_nice, MIN_NICE, MAX_NICE);

        return 0;

err_size:
        put_user(sizeof(*attr), &uattr->size);
        return -E2BIG;
}

/**
 * sys_sched_setscheduler - set/change the scheduler policy and RT priority
 * @pid: the pid in question.
 * @policy: new policy.
 * @param: structure containing the new RT priority.
 *
 * Return: 0 on success. An error code otherwise.
 */
SYSCALL_DEFINE3(sched_setscheduler, pid_t, pid, int, policy, struct sched_param __user *, param)
{
        if (policy < 0)
                return -EINVAL;

        return do_sched_setscheduler(pid, policy, param);
}

/**
 * sys_sched_setparam - set/change the RT priority of a thread
 * @pid: the pid in question.
 * @param: structure containing the new RT priority.
 *
 * Return: 0 on success. An error code otherwise.
 */
SYSCALL_DEFINE2(sched_setparam, pid_t, pid, struct sched_param __user *, param)
{
        return do_sched_setscheduler(pid, SETPARAM_POLICY, param);
}

/**
 * sys_sched_setattr - same as above, but with extended sched_attr
 * @pid: the pid in question.
 * @uattr: structure containing the extended parameters.
 * @flags: for future extension.
 */
SYSCALL_DEFINE3(sched_setattr, pid_t, pid, struct sched_attr __user *, uattr,
                               unsigned int, flags)
{
        struct sched_attr attr;
        struct task_struct *p;
        int retval;

        if (!uattr || pid < 0 || flags)
                return -EINVAL;

        retval = sched_copy_attr(uattr, &attr);
        if (retval)
                return retval;

        if ((int)attr.sched_policy < 0)
                return -EINVAL;
        if (attr.sched_flags & SCHED_FLAG_KEEP_POLICY)
                attr.sched_policy = SETPARAM_POLICY;

        rcu_read_lock();
        retval = -ESRCH;
        p = find_process_by_pid(pid);
        if (likely(p))
                get_task_struct(p);
        rcu_read_unlock();

        if (likely(p)) {
                retval = sched_setattr(p, &attr);
                put_task_struct(p);
        }

        return retval;
}

/**
 * sys_sched_getscheduler - get the policy (scheduling class) of a thread
 * @pid: the pid in question.
 *
 * Return: On success, the policy of the thread. Otherwise, a negative error
 * code.
 */
SYSCALL_DEFINE1(sched_getscheduler, pid_t, pid)
{
        struct task_struct *p;
        int retval;

        if (pid < 0)
                return -EINVAL;

        retval = -ESRCH;
        rcu_read_lock();
        p = find_process_by_pid(pid);
        if (p) {
                retval = security_task_getscheduler(p);
                if (!retval)
                        retval = p->policy
                                | (p->sched_reset_on_fork ? SCHED_RESET_ON_FORK : 0);
        }
        rcu_read_unlock();
        return retval;
}

/**
 * sys_sched_getparam - get the RT priority of a thread
 * @pid: the pid in question.
 * @param: structure containing the RT priority.
 *
 * Return: On success, 0 and the RT priority is in @param. Otherwise, an error
 * code.
 */
SYSCALL_DEFINE2(sched_getparam, pid_t, pid, struct sched_param __user *, param)
{
        struct sched_param lp = { .sched_priority = 0 };
        struct task_struct *p;
        int retval;

        if (!param || pid < 0)
                return -EINVAL;

        rcu_read_lock();
        p = find_process_by_pid(pid);
        retval = -ESRCH;
        if (!p)
                goto out_unlock;

        retval = security_task_getscheduler(p);
        if (retval)
                goto out_unlock;

        if (task_has_rt_policy(p))
                lp.sched_priority = p->rt_priority;
        rcu_read_unlock();

        /*
         * This one might sleep, we cannot do it with a spinlock held ...
         */
        retval = copy_to_user(param, &lp, sizeof(*param)) ? -EFAULT : 0;

        return retval;

out_unlock:
        rcu_read_unlock();
        return retval;
}

/*
 * Copy the kernel size attribute structure (which might be larger
 * than what user-space knows about) to user-space.
 *
 * Note that all cases are valid: user-space buffer can be larger or
 * smaller than the kernel-space buffer. The usual case is that both
 * have the same size.
 */
static int
sched_attr_copy_to_user(struct sched_attr __user *uattr,
                        struct sched_attr *kattr,
                        unsigned int usize)
{
        unsigned int ksize = sizeof(*kattr);

        if (!access_ok(uattr, usize))
                return -EFAULT;

        /*
         * sched_getattr() ABI forwards and backwards compatibility:
         *
         * If usize == ksize then we just copy everything to user-space and all is good.
         *
         * If usize < ksize then we only copy as much as user-space has space for,
         * this keeps ABI compatibility as well. We skip the rest.
         *
         * If usize > ksize then user-space is using a newer version of the ABI,
         * which part the kernel doesn't know about. Just ignore it - tooling can
         * detect the kernel's knowledge of attributes from the attr->size value
         * which is set to ksize in this case.
         */
        kattr->size = min(usize, ksize);

        if (copy_to_user(uattr, kattr, kattr->size))
                return -EFAULT;

        return 0;
}

/**
 * sys_sched_getattr - similar to sched_getparam, but with sched_attr
 * @pid: the pid in question.
 * @uattr: structure containing the extended parameters.
 * @usize: sizeof(attr) for fwd/bwd comp.
 * @flags: for future extension.
 */
SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
                unsigned int, usize, unsigned int, flags)
{
        struct sched_attr kattr = { };
        struct task_struct *p;
        int retval;

        if (!uattr || pid < 0 || usize > PAGE_SIZE ||
            usize < SCHED_ATTR_SIZE_VER0 || flags)
                return -EINVAL;

        rcu_read_lock();
        p = find_process_by_pid(pid);
        retval = -ESRCH;
        if (!p)
                goto out_unlock;

        retval = security_task_getscheduler(p);
        if (retval)
                goto out_unlock;

        kattr.sched_policy = p->policy;
        if (p->sched_reset_on_fork)
                kattr.sched_flags |= SCHED_FLAG_RESET_ON_FORK;
        if (task_has_dl_policy(p))
                __getparam_dl(p, &kattr);
        else if (task_has_rt_policy(p))
                kattr.sched_priority = p->rt_priority;
        else
                kattr.sched_nice = task_nice(p);

#ifdef CONFIG_UCLAMP_TASK
        kattr.sched_util_min = p->uclamp_req[UCLAMP_MIN].value;
        kattr.sched_util_max = p->uclamp_req[UCLAMP_MAX].value;
#endif

        rcu_read_unlock();

        return sched_attr_copy_to_user(uattr, &kattr, usize);

out_unlock:
        rcu_read_unlock();
        return retval;
}

long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
{
        cpumask_var_t cpus_allowed, new_mask;
        struct task_struct *p;
        int retval;

        rcu_read_lock();

        p = find_process_by_pid(pid);
        if (!p) {
                rcu_read_unlock();
                return -ESRCH;
        }

        /* Prevent p going away */
        get_task_struct(p);
        rcu_read_unlock();

        if (p->flags & PF_NO_SETAFFINITY) {
                retval = -EINVAL;
                goto out_put_task;
        }
        if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL)) {
                retval = -ENOMEM;
                goto out_put_task;
        }
        if (!alloc_cpumask_var(&new_mask, GFP_KERNEL)) {
                retval = -ENOMEM;
                goto out_free_cpus_allowed;
        }
        retval = -EPERM;
        if (!check_same_owner(p)) {
                rcu_read_lock();
                if (!ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE)) {
                        rcu_read_unlock();
                        goto out_free_new_mask;
                }
                rcu_read_unlock();
        }

        retval = security_task_setscheduler(p);
        if (retval)
                goto out_free_new_mask;


        cpuset_cpus_allowed(p, cpus_allowed);
        cpumask_and(new_mask, in_mask, cpus_allowed);

        /*
         * Since bandwidth control happens on root_domain basis,
         * if admission test is enabled, we only admit -deadline
         * tasks allowed to run on all the CPUs in the task's
         * root_domain.
         */
#ifdef CONFIG_SMP
        if (task_has_dl_policy(p) && dl_bandwidth_enabled()) {
                rcu_read_lock();
                if (!cpumask_subset(task_rq(p)->rd->span, new_mask)) {
                        retval = -EBUSY;
                        rcu_read_unlock();
                        goto out_free_new_mask;
                }
                rcu_read_unlock();
        }
#endif
again:
        retval = __set_cpus_allowed_ptr(p, new_mask, true);

        if (!retval) {
                cpuset_cpus_allowed(p, cpus_allowed);
                if (!cpumask_subset(new_mask, cpus_allowed)) {
                        /*
                         * We must have raced with a concurrent cpuset
                         * update. Just reset the cpus_allowed to the
                         * cpuset's cpus_allowed
                         */
                        cpumask_copy(new_mask, cpus_allowed);
                        goto again;
                }
        }
out_free_new_mask:
        free_cpumask_var(new_mask);
out_free_cpus_allowed:
        free_cpumask_var(cpus_allowed);
out_put_task:
        put_task_struct(p);
        return retval;
}

static int get_user_cpu_mask(unsigned long __user *user_mask_ptr, unsigned len,
                             struct cpumask *new_mask)
{
        if (len < cpumask_size())
                cpumask_clear(new_mask);
        else if (len > cpumask_size())
                len = cpumask_size();

        return copy_from_user(new_mask, user_mask_ptr, len) ? -EFAULT : 0;
}

/**
 * sys_sched_setaffinity - set the CPU affinity of a process
 * @pid: pid of the process
 * @len: length in bytes of the bitmask pointed to by user_mask_ptr
 * @user_mask_ptr: user-space pointer to the new CPU mask
 *
 * Return: 0 on success. An error code otherwise.
 */
SYSCALL_DEFINE3(sched_setaffinity, pid_t, pid, unsigned int, len,
                unsigned long __user *, user_mask_ptr)
{
        cpumask_var_t new_mask;
        int retval;

        if (!alloc_cpumask_var(&new_mask, GFP_KERNEL))
                return -ENOMEM;

        retval = get_user_cpu_mask(user_mask_ptr, len, new_mask);
        if (retval == 0)
                retval = sched_setaffinity(pid, new_mask);
        free_cpumask_var(new_mask);
        return retval;
}

long sched_getaffinity(pid_t pid, struct cpumask *mask)
{
        struct task_struct *p;
        unsigned long flags;
        int retval;

        rcu_read_lock();

        retval = -ESRCH;
        p = find_process_by_pid(pid);
        if (!p)
                goto out_unlock;

        retval = security_task_getscheduler(p);
        if (retval)
                goto out_unlock;

        raw_spin_lock_irqsave(&p->pi_lock, flags);
        cpumask_and(mask, &p->cpus_mask, cpu_active_mask);
        raw_spin_unlock_irqrestore(&p->pi_lock, flags);

out_unlock:
        rcu_read_unlock();

        return retval;
}

/**
 * sys_sched_getaffinity - get the CPU affinity of a process
 * @pid: pid of the process
 * @len: length in bytes of the bitmask pointed to by user_mask_ptr
 * @user_mask_ptr: user-space pointer to hold the current CPU mask
 *
 * Return: size of CPU mask copied to user_mask_ptr on success. An
 * error code otherwise.
 */
SYSCALL_DEFINE3(sched_getaffinity, pid_t, pid, unsigned int, len,
                unsigned long __user *, user_mask_ptr)
{
        int ret;
        cpumask_var_t mask;

        if ((len * BITS_PER_BYTE) < nr_cpu_ids)
                return -EINVAL;
        if (len & (sizeof(unsigned long)-1))
                return -EINVAL;

        if (!alloc_cpumask_var(&mask, GFP_KERNEL))
                return -ENOMEM;

        ret = sched_getaffinity(pid, mask);
        if (ret == 0) {
                unsigned int retlen = min(len, cpumask_size());

                if (copy_to_user(user_mask_ptr, mask, retlen))
                        ret = -EFAULT;
                else
                        ret = retlen;
        }
        free_cpumask_var(mask);

        return ret;
}

/**
 * sys_sched_yield - yield the current processor to other threads.
 *
 * This function yields the current CPU to other tasks. If there are no
 * other threads running on this CPU then this function will return.
 *
 * Return: 0.
 */
static void do_sched_yield(void)
{
        struct rq_flags rf;
        struct rq *rq;

        rq = this_rq_lock_irq(&rf);

        schedstat_inc(rq->yld_count);
        current->sched_class->yield_task(rq);

        /*
         * Since we are going to call schedule() anyway, there's
         * no need to preempt or enable interrupts:
         */
        preempt_disable();
        rq_unlock(rq, &rf);
        sched_preempt_enable_no_resched();

        schedule();
}

SYSCALL_DEFINE0(sched_yield)
{
        do_sched_yield();
        return 0;
}

#ifndef CONFIG_PREEMPTION
int __sched _cond_resched(void)
{
        if (should_resched(0)) {
                preempt_schedule_common();
                return 1;
        }
        rcu_all_qs();
        return 0;
}
EXPORT_SYMBOL(_cond_resched);
#endif

/*
 * __cond_resched_lock() - if a reschedule is pending, drop the given lock,
 * call schedule, and on return reacquire the lock.
 *
 * This works OK both with and without CONFIG_PREEMPTION. We do strange low-level
 * operations here to prevent schedule() from being called twice (once via
 * spin_unlock(), once by hand).
 */
int __cond_resched_lock(spinlock_t *lock)
{
        int resched = should_resched(PREEMPT_LOCK_OFFSET);
        int ret = 0;

        lockdep_assert_held(lock);

        if (spin_needbreak(lock) || resched) {
                spin_unlock(lock);
                if (resched)
                        preempt_schedule_common();
                else
                        cpu_relax();
                ret = 1;
                spin_lock(lock);
        }
        return ret;
}
EXPORT_SYMBOL(__cond_resched_lock);

/**
 * yield - yield the current processor to other threads.
 *
 * Do not ever use this function, there's a 99% chance you're doing it wrong.
 *
 * The scheduler is at all times free to pick the calling task as the most
 * eligible task to run, if removing the yield() call from your code breaks
 * it, its already broken.
 *
 * Typical broken usage is:
 *
 * while (!event)
 *      yield();
 *
 * where one assumes that yield() will let 'the other' process run that will
 * make event true. If the current task is a SCHED_FIFO task that will never
 * happen. Never use yield() as a progress guarantee!!
 *
 * If you want to use yield() to wait for something, use wait_event().
 * If you want to use yield() to be 'nice' for others, use cond_resched().
 * If you still want to use yield(), do not!
 */
void __sched yield(void)
{
        set_current_state(TASK_RUNNING);
        do_sched_yield();
}
EXPORT_SYMBOL(yield);

/**
 * yield_to - yield the current processor to another thread in
 * your thread group, or accelerate that thread toward the
 * processor it's on.
 * @p: target task
 * @preempt: whether task preemption is allowed or not
 *
 * It's the caller's job to ensure that the target task struct
 * can't go away on us before we can do any checks.
 *
 * Return:
 *      true (>0) if we indeed boosted the target task.
 *      false (0) if we failed to boost the target.
 *      -ESRCH if there's no task to yield to.
 */
int __sched yield_to(struct task_struct *p, bool preempt)
{
        struct task_struct *curr = current;
        struct rq *rq, *p_rq;
        unsigned long flags;
        int yielded = 0;

        local_irq_save(flags);
        rq = this_rq();

again:
        p_rq = task_rq(p);
        /*
         * If we're the only runnable task on the rq and target rq also
         * has only one task, there's absolutely no point in yielding.
         */
        if (rq->nr_running == 1 && p_rq->nr_running == 1) {
                yielded = -ESRCH;
                goto out_irq;
        }

        double_rq_lock(rq, p_rq);
        if (task_rq(p) != p_rq) {
                double_rq_unlock(rq, p_rq);
                goto again;
        }

        if (!curr->sched_class->yield_to_task)
                goto out_unlock;

        if (curr->sched_class != p->sched_class)
                goto out_unlock;

        if (task_running(p_rq, p) || p->state)
                goto out_unlock;

        yielded = curr->sched_class->yield_to_task(rq, p, preempt);
        if (yielded) {
                schedstat_inc(rq->yld_count);
                /*
                 * Make p's CPU reschedule; pick_next_entity takes care of
                 * fairness.
                 */
                if (preempt && rq != p_rq)
                        resched_curr(p_rq);
        }

out_unlock:
        double_rq_unlock(rq, p_rq);
out_irq:
        local_irq_restore(flags);

        if (yielded > 0)
                schedule();

        return yielded;
}
EXPORT_SYMBOL_GPL(yield_to);

int io_schedule_prepare(void)
{
        int old_iowait = current->in_iowait;

        current->in_iowait = 1;
        blk_schedule_flush_plug(current);

        return old_iowait;
}

void io_schedule_finish(int token)
{
        current->in_iowait = token;
}

/*
 * This task is about to go to sleep on IO. Increment rq->nr_iowait so
 * that process accounting knows that this is a task in IO wait state.
 */
long __sched io_schedule_timeout(long timeout)
{
        int token;
        long ret;

        token = io_schedule_prepare();
        ret = schedule_timeout(timeout);
        io_schedule_finish(token);

        return ret;
}
EXPORT_SYMBOL(io_schedule_timeout);

void __sched io_schedule(void)
{
        int token;

        token = io_schedule_prepare();
        schedule();
        io_schedule_finish(token);
}
EXPORT_SYMBOL(io_schedule);

/**
 * sys_sched_get_priority_max - return maximum RT priority.
 * @policy: scheduling class.
 *
 * Return: On success, this syscall returns the maximum
 * rt_priority that can be used by a given scheduling class.
 * On failure, a negative error code is returned.
 */
SYSCALL_DEFINE1(sched_get_priority_max, int, policy)
{
        int ret = -EINVAL;

        switch (policy) {
        case SCHED_FIFO:
        case SCHED_RR:
                ret = MAX_USER_RT_PRIO-1;
                break;
        case SCHED_DEADLINE:
        case SCHED_NORMAL:
        case SCHED_BATCH:
        case SCHED_IDLE:
                ret = 0;
                break;
        }
        return ret;
}

/**
 * sys_sched_get_priority_min - return minimum RT priority.
 * @policy: scheduling class.
 *
 * Return: On success, this syscall returns the minimum
 * rt_priority that can be used by a given scheduling class.
 * On failure, a negative error code is returned.
 */
SYSCALL_DEFINE1(sched_get_priority_min, int, policy)
{
        int ret = -EINVAL;

        switch (policy) {
        case SCHED_FIFO:
        case SCHED_RR:
                ret = 1;
                break;
        case SCHED_DEADLINE:
        case SCHED_NORMAL:
        case SCHED_BATCH:
        case SCHED_IDLE:
                ret = 0;
        }
        return ret;
}

static int sched_rr_get_interval(pid_t pid, struct timespec64 *t)
{
        struct task_struct *p;
        unsigned int time_slice;
        struct rq_flags rf;
        struct rq *rq;
        int retval;

        if (pid < 0)
                return -EINVAL;

        retval = -ESRCH;
        rcu_read_lock();
        p = find_process_by_pid(pid);
        if (!p)
                goto out_unlock;

        retval = security_task_getscheduler(p);
        if (retval)
                goto out_unlock;

        rq = task_rq_lock(p, &rf);
        time_slice = 0;
        if (p->sched_class->get_rr_interval)
                time_slice = p->sched_class->get_rr_interval(rq, p);
        task_rq_unlock(rq, p, &rf);

        rcu_read_unlock();
        jiffies_to_timespec64(time_slice, t);
        return 0;

out_unlock:
        rcu_read_unlock();
        return retval;
}

/**
 * sys_sched_rr_get_interval - return the default timeslice of a process.
 * @pid: pid of the process.
 * @interval: userspace pointer to the timeslice value.
 *
 * this syscall writes the default timeslice value of a given process
 * into the user-space timespec buffer. A value of '0' means infinity.
 *
 * Return: On success, 0 and the timeslice is in @interval. Otherwise,
 * an error code.
 */
SYSCALL_DEFINE2(sched_rr_get_interval, pid_t, pid,
                struct __kernel_timespec __user *, interval)
{
        struct timespec64 t;
        int retval = sched_rr_get_interval(pid, &t);

        if (retval == 0)
                retval = put_timespec64(&t, interval);

        return retval;
}

#ifdef CONFIG_COMPAT_32BIT_TIME
SYSCALL_DEFINE2(sched_rr_get_interval_time32, pid_t, pid,
                struct old_timespec32 __user *, interval)
{
        struct timespec64 t;
        int retval = sched_rr_get_interval(pid, &t);

        if (retval == 0)
                retval = put_old_timespec32(&t, interval);
        return retval;
}
#endif

void sched_show_task(struct task_struct *p)
{
        unsigned long free = 0;
        int ppid;

        if (!try_get_task_stack(p))
                return;

        printk(KERN_INFO "%-15.15s %c", p->comm, task_state_to_char(p));

        if (p->state == TASK_RUNNING)
                printk(KERN_CONT "  running task    ");
#ifdef CONFIG_DEBUG_STACK_USAGE
        free = stack_not_used(p);
#endif
        ppid = 0;
        rcu_read_lock();
        if (pid_alive(p))
                ppid = task_pid_nr(rcu_dereference(p->real_parent));
        rcu_read_unlock();
        printk(KERN_CONT "%5lu %5d %6d 0x%08lx\n", free,
                task_pid_nr(p), ppid,
                (unsigned long)task_thread_info(p)->flags);

        print_worker_info(KERN_INFO, p);
        show_stack(p, NULL);
        put_task_stack(p);
}
EXPORT_SYMBOL_GPL(sched_show_task);

static inline bool
state_filter_match(unsigned long state_filter, struct task_struct *p)
{
        /* no filter, everything matches */
        if (!state_filter)
                return true;

        /* filter, but doesn't match */
        if (!(p->state & state_filter))
                return false;

        /*
         * When looking for TASK_UNINTERRUPTIBLE skip TASK_IDLE (allows
         * TASK_KILLABLE).
         */
        if (state_filter == TASK_UNINTERRUPTIBLE && p->state == TASK_IDLE)
                return false;

        return true;
}


void show_state_filter(unsigned long state_filter)
{
        struct task_struct *g, *p;

#if BITS_PER_LONG == 32
        printk(KERN_INFO
                "  task                PC stack   pid father\n");
#else
        printk(KERN_INFO
                "  task                        PC stack   pid father\n");
#endif
        rcu_read_lock();
        for_each_process_thread(g, p) {
                /*
                 * reset the NMI-timeout, listing all files on a slow
                 * console might take a lot of time:
                 * Also, reset softlockup watchdogs on all CPUs, because
                 * another CPU might be blocked waiting for us to process
                 * an IPI.
                 */
                touch_nmi_watchdog();
                touch_all_softlockup_watchdogs();
                if (state_filter_match(state_filter, p))
                        sched_show_task(p);
        }

#ifdef CONFIG_SCHED_DEBUG
        if (!state_filter)
                sysrq_sched_debug_show();
#endif
        rcu_read_unlock();
        /*
         * Only show locks if all tasks are dumped:
         */
        if (!state_filter)
                debug_show_all_locks();
}

/**
 * init_idle - set up an idle thread for a given CPU
 * @idle: task in question
 * @cpu: CPU the idle task belongs to
 *
 * NOTE: this function does not set the idle thread's NEED_RESCHED
 * flag, to make booting more robust.
 */
void init_idle(struct task_struct *idle, int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        unsigned long flags;

        __sched_fork(0, idle);

        raw_spin_lock_irqsave(&idle->pi_lock, flags);
        raw_spin_lock(&rq->lock);

        idle->state = TASK_RUNNING;
        idle->se.exec_start = sched_clock();
        idle->flags |= PF_IDLE;

        kasan_unpoison_task_stack(idle);

#ifdef CONFIG_SMP
        /*
         * Its possible that init_idle() gets called multiple times on a task,
         * in that case do_set_cpus_allowed() will not do the right thing.
         *
         * And since this is boot we can forgo the serialization.
         */
        set_cpus_allowed_common(idle, cpumask_of(cpu));
#endif
        /*
         * We're having a chicken and egg problem, even though we are
         * holding rq->lock, the CPU isn't yet set to this CPU so the
         * lockdep check in task_group() will fail.
         *
         * Similar case to sched_fork(). / Alternatively we could
         * use task_rq_lock() here and obtain the other rq->lock.
         *
         * Silence PROVE_RCU
         */
        rcu_read_lock();
        __set_task_cpu(idle, cpu);
        rcu_read_unlock();

        rq->idle = idle;
        rcu_assign_pointer(rq->curr, idle);
        idle->on_rq = TASK_ON_RQ_QUEUED;
#ifdef CONFIG_SMP
        idle->on_cpu = 1;
#endif
        raw_spin_unlock(&rq->lock);
        raw_spin_unlock_irqrestore(&idle->pi_lock, flags);

        /* Set the preempt count _outside_ the spinlocks! */
        init_idle_preempt_count(idle, cpu);

        /*
         * The idle tasks have their own, simple scheduling class:
         */
        idle->sched_class = &idle_sched_class;
        ftrace_graph_init_idle_task(idle, cpu);
        vtime_init_idle(idle, cpu);
#ifdef CONFIG_SMP
        sprintf(idle->comm, "%s/%d", INIT_TASK_COMM, cpu);
#endif
}

#ifdef CONFIG_SMP

int cpuset_cpumask_can_shrink(const struct cpumask *cur,
                              const struct cpumask *trial)
{
        int ret = 1;

        if (!cpumask_weight(cur))
                return ret;

        ret = dl_cpuset_cpumask_can_shrink(cur, trial);

        return ret;
}

int task_can_attach(struct task_struct *p,
                    const struct cpumask *cs_cpus_allowed)
{
        int ret = 0;

        /*
         * Kthreads which disallow setaffinity shouldn't be moved
         * to a new cpuset; we don't want to change their CPU
         * affinity and isolating such threads by their set of
         * allowed nodes is unnecessary.  Thus, cpusets are not
         * applicable for such threads.  This prevents checking for
         * success of set_cpus_allowed_ptr() on all attached tasks
         * before cpus_mask may be changed.
         */
        if (p->flags & PF_NO_SETAFFINITY) {
                ret = -EINVAL;
                goto out;
        }

        if (dl_task(p) && !cpumask_intersects(task_rq(p)->rd->span,
                                              cs_cpus_allowed))
                ret = dl_task_can_attach(p, cs_cpus_allowed);

out:
        return ret;
}

bool sched_smp_initialized __read_mostly;

#ifdef CONFIG_NUMA_BALANCING
/* Migrate current task p to target_cpu */
int migrate_task_to(struct task_struct *p, int target_cpu)
{
        struct migration_arg arg = { p, target_cpu };
        int curr_cpu = task_cpu(p);

        if (curr_cpu == target_cpu)
                return 0;

        if (!cpumask_test_cpu(target_cpu, p->cpus_ptr))
                return -EINVAL;

        /* TODO: This is not properly updating schedstats */

        trace_sched_move_numa(p, curr_cpu, target_cpu);
        return stop_one_cpu(curr_cpu, migration_cpu_stop, &arg);
}

/*
 * Requeue a task on a given node and accurately track the number of NUMA
 * tasks on the runqueues
 */
void sched_setnuma(struct task_struct *p, int nid)
{
        bool queued, running;
        struct rq_flags rf;
        struct rq *rq;

        rq = task_rq_lock(p, &rf);
        queued = task_on_rq_queued(p);
        running = task_current(rq, p);

        if (queued)
                dequeue_task(rq, p, DEQUEUE_SAVE);
        if (running)
                put_prev_task(rq, p);

        p->numa_preferred_nid = nid;

        if (queued)
                enqueue_task(rq, p, ENQUEUE_RESTORE | ENQUEUE_NOCLOCK);
        if (running)
                set_next_task(rq, p);
        task_rq_unlock(rq, p, &rf);
}
#endif /* CONFIG_NUMA_BALANCING */

#ifdef CONFIG_HOTPLUG_CPU
/*
 * Ensure that the idle task is using init_mm right before its CPU goes
 * offline.
 */
void idle_task_exit(void)
{
        struct mm_struct *mm = current->active_mm;

        BUG_ON(cpu_online(smp_processor_id()));
        BUG_ON(current != this_rq()->idle);

        if (mm != &init_mm) {
                switch_mm(mm, &init_mm, current);
                finish_arch_post_lock_switch();
        }

        /* finish_cpu(), as ran on the BP, will clean up the active_mm state */
}

/*
 * Since this CPU is going 'away' for a while, fold any nr_active delta
 * we might have. Assumes we're called after migrate_tasks() so that the
 * nr_active count is stable. We need to take the teardown thread which
 * is calling this into account, so we hand in adjust = 1 to the load
 * calculation.
 *
 * Also see the comment "Global load-average calculations".
 */
static void calc_load_migrate(struct rq *rq)
{
        long delta = calc_load_fold_active(rq, 1);
        if (delta)
                atomic_long_add(delta, &calc_load_tasks);
}

static struct task_struct *__pick_migrate_task(struct rq *rq)
{
        const struct sched_class *class;
        struct task_struct *next;

        for_each_class(class) {
                next = class->pick_next_task(rq);
                if (next) {
                        next->sched_class->put_prev_task(rq, next);
                        return next;
                }
        }

        /* The idle class should always have a runnable task */
        BUG();
}

/*
 * Migrate all tasks from the rq, sleeping tasks will be migrated by
 * try_to_wake_up()->select_task_rq().
 *
 * Called with rq->lock held even though we'er in stop_machine() and
 * there's no concurrency possible, we hold the required locks anyway
 * because of lock validation efforts.
 */
static void migrate_tasks(struct rq *dead_rq, struct rq_flags *rf)
{
        struct rq *rq = dead_rq;
        struct task_struct *next, *stop = rq->stop;
        struct rq_flags orf = *rf;
        int dest_cpu;

        /*
         * Fudge the rq selection such that the below task selection loop
         * doesn't get stuck on the currently eligible stop task.
         *
         * We're currently inside stop_machine() and the rq is either stuck
         * in the stop_machine_cpu_stop() loop, or we're executing this code,
         * either way we should never end up calling schedule() until we're
         * done here.
         */
        rq->stop = NULL;

        /*
         * put_prev_task() and pick_next_task() sched
         * class method both need to have an up-to-date
         * value of rq->clock[_task]
         */
        update_rq_clock(rq);

        for (;;) {
                /*
                 * There's this thread running, bail when that's the only
                 * remaining thread:
                 */
                if (rq->nr_running == 1)
                        break;

                next = __pick_migrate_task(rq);

                /*
                 * Rules for changing task_struct::cpus_mask are holding
                 * both pi_lock and rq->lock, such that holding either
                 * stabilizes the mask.
                 *
                 * Drop rq->lock is not quite as disastrous as it usually is
                 * because !cpu_active at this point, which means load-balance
                 * will not interfere. Also, stop-machine.
                 */
                rq_unlock(rq, rf);
                raw_spin_lock(&next->pi_lock);
                rq_relock(rq, rf);

                /*
                 * Since we're inside stop-machine, _nothing_ should have
                 * changed the task, WARN if weird stuff happened, because in
                 * that case the above rq->lock drop is a fail too.
                 */
                if (WARN_ON(task_rq(next) != rq || !task_on_rq_queued(next))) {
                        raw_spin_unlock(&next->pi_lock);
                        continue;
                }

                /* Find suitable destination for @next, with force if needed. */
                dest_cpu = select_fallback_rq(dead_rq->cpu, next);
                rq = __migrate_task(rq, rf, next, dest_cpu);
                if (rq != dead_rq) {
                        rq_unlock(rq, rf);
                        rq = dead_rq;
                        *rf = orf;
                        rq_relock(rq, rf);
                }
                raw_spin_unlock(&next->pi_lock);
        }

        rq->stop = stop;
}
#endif /* CONFIG_HOTPLUG_CPU */

void set_rq_online(struct rq *rq)
{
        if (!rq->online) {
                const struct sched_class *class;

                cpumask_set_cpu(rq->cpu, rq->rd->online);
                rq->online = 1;

                for_each_class(class) {
                        if (class->rq_online)
                                class->rq_online(rq);
                }
        }
}

void set_rq_offline(struct rq *rq)
{
        if (rq->online) {
                const struct sched_class *class;

                for_each_class(class) {
                        if (class->rq_offline)
                                class->rq_offline(rq);
                }

                cpumask_clear_cpu(rq->cpu, rq->rd->online);
                rq->online = 0;
        }
}

/*
 * used to mark begin/end of suspend/resume:
 */
static int num_cpus_frozen;

/*
 * Update cpusets according to cpu_active mask.  If cpusets are
 * disabled, cpuset_update_active_cpus() becomes a simple wrapper
 * around partition_sched_domains().
 *
 * If we come here as part of a suspend/resume, don't touch cpusets because we
 * want to restore it back to its original state upon resume anyway.
 */
static void cpuset_cpu_active(void)
{
        if (cpuhp_tasks_frozen) {
                /*
                 * num_cpus_frozen tracks how many CPUs are involved in suspend
                 * resume sequence. As long as this is not the last online
                 * operation in the resume sequence, just build a single sched
                 * domain, ignoring cpusets.
                 */
                partition_sched_domains(1, NULL, NULL);
                if (--num_cpus_frozen)
                        return;
                /*
                 * This is the last CPU online operation. So fall through and
                 * restore the original sched domains by considering the
                 * cpuset configurations.
                 */
                cpuset_force_rebuild();
        }
        cpuset_update_active_cpus();
}

static int cpuset_cpu_inactive(unsigned int cpu)
{
        if (!cpuhp_tasks_frozen) {
                if (dl_cpu_busy(cpu))
                        return -EBUSY;
                cpuset_update_active_cpus();
        } else {
                num_cpus_frozen++;
                partition_sched_domains(1, NULL, NULL);
        }
        return 0;
}

int sched_cpu_activate(unsigned int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        struct rq_flags rf;

#ifdef CONFIG_SCHED_SMT
        /*
         * When going up, increment the number of cores with SMT present.
         */
        if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
                static_branch_inc_cpuslocked(&sched_smt_present);
#endif
        set_cpu_active(cpu, true);

        if (sched_smp_initialized) {
                sched_domains_numa_masks_set(cpu);
                cpuset_cpu_active();
        }

        /*
         * Put the rq online, if not already. This happens:
         *
         * 1) In the early boot process, because we build the real domains
         *    after all CPUs have been brought up.
         *
         * 2) At runtime, if cpuset_cpu_active() fails to rebuild the
         *    domains.
         */
        rq_lock_irqsave(rq, &rf);
        if (rq->rd) {
                BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
                set_rq_online(rq);
        }
        rq_unlock_irqrestore(rq, &rf);

        return 0;
}

int sched_cpu_deactivate(unsigned int cpu)
{
        int ret;

        set_cpu_active(cpu, false);
        /*
         * We've cleared cpu_active_mask, wait for all preempt-disabled and RCU
         * users of this state to go away such that all new such users will
         * observe it.
         *
         * Do sync before park smpboot threads to take care the rcu boost case.
         */
        synchronize_rcu();

#ifdef CONFIG_SCHED_SMT
        /*
         * When going down, decrement the number of cores with SMT present.
         */
        if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
                static_branch_dec_cpuslocked(&sched_smt_present);
#endif

        if (!sched_smp_initialized)
                return 0;

        ret = cpuset_cpu_inactive(cpu);
        if (ret) {
                set_cpu_active(cpu, true);
                return ret;
        }
        sched_domains_numa_masks_clear(cpu);
        return 0;
}

static void sched_rq_cpu_starting(unsigned int cpu)
{
        struct rq *rq = cpu_rq(cpu);

        rq->calc_load_update = calc_load_update;
        update_max_interval();
}

int sched_cpu_starting(unsigned int cpu)
{
        sched_rq_cpu_starting(cpu);
        sched_tick_start(cpu);
        return 0;
}

#ifdef CONFIG_HOTPLUG_CPU
int sched_cpu_dying(unsigned int cpu)
{
        struct rq *rq = cpu_rq(cpu);
        struct rq_flags rf;

        /* Handle pending wakeups and then migrate everything off */
        sched_ttwu_pending();
        sched_tick_stop(cpu);

        rq_lock_irqsave(rq, &rf);
        if (rq->rd) {
                BUG_ON(!cpumask_test_cpu(cpu, rq->rd->span));
                set_rq_offline(rq);
        }
        migrate_tasks(rq, &rf);
        BUG_ON(rq->nr_running != 1);
        rq_unlock_irqrestore(rq, &rf);

        calc_load_migrate(rq);
        update_max_interval();
        nohz_balance_exit_idle(rq);
        hrtick_clear(rq);
        return 0;
}
#endif

void __init sched_init_smp(void)
{
        sched_init_numa();

        /*
         * There's no userspace yet to cause hotplug operations; hence all the
         * CPU masks are stable and all blatant races in the below code cannot
         * happen.
         */
        mutex_lock(&sched_domains_mutex);
        sched_init_domains(cpu_active_mask);
        mutex_unlock(&sched_domains_mutex);

        /* Move init over to a non-isolated CPU */
        if (set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_FLAG_DOMAIN)) < 0)
                BUG();
        sched_init_granularity();

        init_sched_rt_class();
        init_sched_dl_class();

        sched_smp_initialized = true;
}

static int __init migration_init(void)
{
        sched_cpu_starting(smp_processor_id());
        return 0;
}
early_initcall(migration_init);

#else
void __init sched_init_smp(void)
{
        sched_init_granularity();
}
#endif /* CONFIG_SMP */

int in_sched_functions(unsigned long addr)
{
        return in_lock_functions(addr) ||
                (addr >= (unsigned long)__sched_text_start
                && addr < (unsigned long)__sched_text_end);
}

#ifdef CONFIG_CGROUP_SCHED
/*
 * Default task group.
 * Every task in system belongs to this group at bootup.
 */
struct task_group root_task_group;
LIST_HEAD(task_groups);

/* Cacheline aligned slab cache for task_group */
static struct kmem_cache *task_group_cache __read_mostly;
#endif

DECLARE_PER_CPU(cpumask_var_t, load_balance_mask);
DECLARE_PER_CPU(cpumask_var_t, select_idle_mask);

void __init sched_init(void)
{
        unsigned long ptr = 0;
        int i;

        wait_bit_init();

#ifdef CONFIG_FAIR_GROUP_SCHED
        ptr += 2 * nr_cpu_ids * sizeof(void **);
#endif
#ifdef CONFIG_RT_GROUP_SCHED
        ptr += 2 * nr_cpu_ids * sizeof(void **);
#endif
        if (ptr) {
                ptr = (unsigned long)kzalloc(ptr, GFP_NOWAIT);

#ifdef CONFIG_FAIR_GROUP_SCHED
                root_task_group.se = (struct sched_entity **)ptr;
                ptr += nr_cpu_ids * sizeof(void **);

                root_task_group.cfs_rq = (struct cfs_rq **)ptr;
                ptr += nr_cpu_ids * sizeof(void **);

                root_task_group.shares = ROOT_TASK_GROUP_LOAD;
                init_cfs_bandwidth(&root_task_group.cfs_bandwidth);
#endif /* CONFIG_FAIR_GROUP_SCHED */
#ifdef CONFIG_RT_GROUP_SCHED
                root_task_group.rt_se = (struct sched_rt_entity **)ptr;
                ptr += nr_cpu_ids * sizeof(void **);

                root_task_group.rt_rq = (struct rt_rq **)ptr;
                ptr += nr_cpu_ids * sizeof(void **);

#endif /* CONFIG_RT_GROUP_SCHED */
        }
#ifdef CONFIG_CPUMASK_OFFSTACK
        for_each_possible_cpu(i) {
                per_cpu(load_balance_mask, i) = (cpumask_var_t)kzalloc_node(
                        cpumask_size(), GFP_KERNEL, cpu_to_node(i));
                per_cpu(select_idle_mask, i) = (cpumask_var_t)kzalloc_node(
                        cpumask_size(), GFP_KERNEL, cpu_to_node(i));
        }
#endif /* CONFIG_CPUMASK_OFFSTACK */

        init_rt_bandwidth(&def_rt_bandwidth, global_rt_period(), global_rt_runtime());
        init_dl_bandwidth(&def_dl_bandwidth, global_rt_period(), global_rt_runtime());

#ifdef CONFIG_SMP
        init_defrootdomain();
#endif

#ifdef CONFIG_RT_GROUP_SCHED
        init_rt_bandwidth(&root_task_group.rt_bandwidth,
                        global_rt_period(), global_rt_runtime());
#endif /* CONFIG_RT_GROUP_SCHED */

#ifdef CONFIG_CGROUP_SCHED
        task_group_cache = KMEM_CACHE(task_group, 0);

        list_add(&root_task_group.list, &task_groups);
        INIT_LIST_HEAD(&root_task_group.children);
        INIT_LIST_HEAD(&root_task_group.siblings);
        autogroup_init(&init_task);
#endif /* CONFIG_CGROUP_SCHED */

        for_each_possible_cpu(i) {
                struct rq *rq;

                rq = cpu_rq(i);
                raw_spin_lock_init(&rq->lock);
                rq->nr_running = 0;
                rq->calc_load_active = 0;
                rq->calc_load_update = jiffies + LOAD_FREQ;
                init_cfs_rq(&rq->cfs);
                init_rt_rq(&rq->rt);
                init_dl_rq(&rq->dl);
#ifdef CONFIG_FAIR_GROUP_SCHED
                INIT_LIST_HEAD(&rq->leaf_cfs_rq_list);
                rq->tmp_alone_branch = &rq->leaf_cfs_rq_list;
                /*
                 * How much CPU bandwidth does root_task_group get?
                 *
                 * In case of task-groups formed thr' the cgroup filesystem, it
                 * gets 100% of the CPU resources in the system. This overall
                 * system CPU resource is divided among the tasks of
                 * root_task_group and its child task-groups in a fair manner,
                 * based on each entity's (task or task-group's) weight
                 * (se->load.weight).
                 *
                 * In other words, if root_task_group has 10 tasks of weight
                 * 1024) and two child groups A0 and A1 (of weight 1024 each),
                 * then A0's share of the CPU resource is:
                 *
                 *      A0's bandwidth = 1024 / (10*1024 + 1024 + 1024) = 8.33%
                 *
                 * We achieve this by letting root_task_group's tasks sit
                 * directly in rq->cfs (i.e root_task_group->se[] = NULL).
                 */
                init_tg_cfs_entry(&root_task_group, &rq->cfs, NULL, i, NULL);
#endif /* CONFIG_FAIR_GROUP_SCHED */

                rq->rt.rt_runtime = def_rt_bandwidth.rt_runtime;
#ifdef CONFIG_RT_GROUP_SCHED
                init_tg_rt_entry(&root_task_group, &rq->rt, NULL, i, NULL);
#endif
#ifdef CONFIG_SMP
                rq->sd = NULL;
                rq->rd = NULL;
                rq->cpu_capacity = rq->cpu_capacity_orig = SCHED_CAPACITY_SCALE;
                rq->balance_callback = NULL;
                rq->active_balance = 0;
                rq->next_balance = jiffies;
                rq->push_cpu = 0;
                rq->cpu = i;
                rq->online = 0;
                rq->idle_stamp = 0;
                rq->avg_idle = 2*sysctl_sched_migration_cost;
                rq->max_idle_balance_cost = sysctl_sched_migration_cost;

                rq_csd_init(rq, &rq->wake_csd, wake_csd_func);

                INIT_LIST_HEAD(&rq->cfs_tasks);

                rq_attach_root(rq, &def_root_domain);
#ifdef CONFIG_NO_HZ_COMMON
                rq->last_blocked_load_update_tick = jiffies;
                atomic_set(&rq->nohz_flags, 0);

                rq_csd_init(rq, &rq->nohz_csd, nohz_csd_func);
#endif
#endif /* CONFIG_SMP */
                hrtick_rq_init(rq);
                atomic_set(&rq->nr_iowait, 0);
        }

        set_load_weight(&init_task, false);

        /*
         * The boot idle thread does lazy MMU switching as well:
         */
        mmgrab(&init_mm);
        enter_lazy_tlb(&init_mm, current);

        /*
         * Make us the idle thread. Technically, schedule() should not be
         * called from this thread, however somewhere below it might be,
         * but because we are the idle thread, we just pick up running again
         * when this runqueue becomes "idle".
         */
        init_idle(current, smp_processor_id());

        calc_load_update = jiffies + LOAD_FREQ;

#ifdef CONFIG_SMP
        idle_thread_set_boot_cpu();
#endif
        init_sched_fair_class();

        init_schedstats();

        psi_init();

        init_uclamp();

        scheduler_running = 1;
}

#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
static inline int preempt_count_equals(int preempt_offset)
{
        int nested = preempt_count() + rcu_preempt_depth();

        return (nested == preempt_offset);
}

void __might_sleep(const char *file, int line, int preempt_offset)
{
        /*
         * Blocking primitives will set (and therefore destroy) current->state,
         * since we will exit with TASK_RUNNING make sure we enter with it,
         * otherwise we will destroy state.
         */
        WARN_ONCE(current->state != TASK_RUNNING && current->task_state_change,
                        "do not call blocking ops when !TASK_RUNNING; "
                        "state=%lx set at [<%p>] %pS\n",
                        current->state,
                        (void *)current->task_state_change,
                        (void *)current->task_state_change);

        ___might_sleep(file, line, preempt_offset);
}
EXPORT_SYMBOL(__might_sleep);

void ___might_sleep(const char *file, int line, int preempt_offset)
{
        /* Ratelimiting timestamp: */
        static unsigned long prev_jiffy;

        unsigned long preempt_disable_ip;

        /* WARN_ON_ONCE() by default, no rate limit required: */
        rcu_sleep_check();

        if ((preempt_count_equals(preempt_offset) && !irqs_disabled() &&
             !is_idle_task(current) && !current->non_block_count) ||
            system_state == SYSTEM_BOOTING || system_state > SYSTEM_RUNNING ||
            oops_in_progress)
                return;

        if (time_before(jiffies, prev_jiffy + HZ) && prev_jiffy)
                return;
        prev_jiffy = jiffies;

        /* Save this before calling printk(), since that will clobber it: */
        preempt_disable_ip = get_preempt_disable_ip(current);

        printk(KERN_ERR
                "BUG: sleeping function called from invalid context at %s:%d\n",
                        file, line);
        printk(KERN_ERR
                "in_atomic(): %d, irqs_disabled(): %d, non_block: %d, pid: %d, name: %s\n",
                        in_atomic(), irqs_disabled(), current->non_block_count,
                        current->pid, current->comm);

        if (task_stack_end_corrupted(current))
                printk(KERN_EMERG "Thread overran stack, or stack corrupted\n");

        debug_show_held_locks(current);
        if (irqs_disabled())
                print_irqtrace_events(current);
        if (IS_ENABLED(CONFIG_DEBUG_PREEMPT)
            && !preempt_count_equals(preempt_offset)) {
                pr_err("Preemption disabled at:");
                print_ip_sym(preempt_disable_ip);
                pr_cont("\n");
        }
        dump_stack();
        add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
}
EXPORT_SYMBOL(___might_sleep);

void __cant_sleep(const char *file, int line, int preempt_offset)
{
        static unsigned long prev_jiffy;

        if (irqs_disabled())
                return;

        if (!IS_ENABLED(CONFIG_PREEMPT_COUNT))
                return;

        if (preempt_count() > preempt_offset)
                return;

        if (time_before(jiffies, prev_jiffy + HZ) && prev_jiffy)
                return;
        prev_jiffy = jiffies;

        printk(KERN_ERR "BUG: assuming atomic context at %s:%d\n", file, line);
        printk(KERN_ERR "in_atomic(): %d, irqs_disabled(): %d, pid: %d, name: %s\n",
                        in_atomic(), irqs_disabled(),
                        current->pid, current->comm);

        debug_show_held_locks(current);
        dump_stack();
        add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
}
EXPORT_SYMBOL_GPL(__cant_sleep);
#endif

#ifdef CONFIG_MAGIC_SYSRQ
void normalize_rt_tasks(void)
{
        struct task_struct *g, *p;
        struct sched_attr attr = {
                .sched_policy = SCHED_NORMAL,
        };

        read_lock(&tasklist_lock);
        for_each_process_thread(g, p) {
                /*
                 * Only normalize user tasks:
                 */
                if (p->flags & PF_KTHREAD)
                        continue;

                p->se.exec_start = 0;
                schedstat_set(p->se.statistics.wait_start,  0);
                schedstat_set(p->se.statistics.sleep_start, 0);
                schedstat_set(p->se.statistics.block_start, 0);

                if (!dl_task(p) && !rt_task(p)) {
                        /*
                         * Renice negative nice level userspace
                         * tasks back to 0:
                         */
                        if (task_nice(p) < 0)
                                set_user_nice(p, 0);
                        continue;
                }

                __sched_setscheduler(p, &attr, false, false);
        }
        read_unlock(&tasklist_lock);
}

#endif /* CONFIG_MAGIC_SYSRQ */

#if defined(CONFIG_IA64) || defined(CONFIG_KGDB_KDB)
/*
 * These functions are only useful for the IA64 MCA handling, or kdb.
 *
 * They can only be called when the whole system has been
 * stopped - every CPU needs to be quiescent, and no scheduling
 * activity can take place. Using them for anything else would
 * be a serious bug, and as a result, they aren't even visible
 * under any other configuration.
 */

/**
 * curr_task - return the current task for a given CPU.
 * @cpu: the processor in question.
 *
 * ONLY VALID WHEN THE WHOLE SYSTEM IS STOPPED!
 *
 * Return: The current task for @cpu.
 */
struct task_struct *curr_task(int cpu)
{
        return cpu_curr(cpu);
}

#endif /* defined(CONFIG_IA64) || defined(CONFIG_KGDB_KDB) */

#ifdef CONFIG_IA64
/**
 * ia64_set_curr_task - set the current task for a given CPU.
 * @cpu: the processor in question.
 * @p: the task pointer to set.
 *
 * Description: This function must only be used when non-maskable interrupts
 * are serviced on a separate stack. It allows the architecture to switch the
 * notion of the current task on a CPU in a non-blocking manner. This function
 * must be called with all CPU's synchronized, and interrupts disabled, the
 * and caller must save the original value of the current task (see
 * curr_task() above) and restore that value before reenabling interrupts and
 * re-starting the system.
 *
 * ONLY VALID WHEN THE WHOLE SYSTEM IS STOPPED!
 */
void ia64_set_curr_task(int cpu, struct task_struct *p)
{
        cpu_curr(cpu) = p;
}

#endif

#ifdef CONFIG_CGROUP_SCHED
/* task_group_lock serializes the addition/removal of task groups */
static DEFINE_SPINLOCK(task_group_lock);

static inline void alloc_uclamp_sched_group(struct task_group *tg,
                                            struct task_group *parent)
{
#ifdef CONFIG_UCLAMP_TASK_GROUP
        enum uclamp_id clamp_id;

        for_each_clamp_id(clamp_id) {
                uclamp_se_set(&tg->uclamp_req[clamp_id],
                              uclamp_none(clamp_id), false);
                tg->uclamp[clamp_id] = parent->uclamp[clamp_id];
        }
#endif
}

static void sched_free_group(struct task_group *tg)
{
        free_fair_sched_group(tg);
        free_rt_sched_group(tg);
        autogroup_free(tg);
        kmem_cache_free(task_group_cache, tg);
}

/* allocate runqueue etc for a new task group */
struct task_group *sched_create_group(struct task_group *parent)
{
        struct task_group *tg;

        tg = kmem_cache_alloc(task_group_cache, GFP_KERNEL | __GFP_ZERO);
        if (!tg)
                return ERR_PTR(-ENOMEM);

        if (!alloc_fair_sched_group(tg, parent))
                goto err;

        if (!alloc_rt_sched_group(tg, parent))
                goto err;

        alloc_uclamp_sched_group(tg, parent);

        return tg;

err:
        sched_free_group(tg);
        return ERR_PTR(-ENOMEM);
}

void sched_online_group(struct task_group *tg, struct task_group *parent)
{
        unsigned long flags;

        spin_lock_irqsave(&task_group_lock, flags);
        list_add_rcu(&tg->list, &task_groups);

        /* Root should already exist: */
        WARN_ON(!parent);

        tg->parent = parent;
        INIT_LIST_HEAD(&tg->children);
        list_add_rcu(&tg->siblings, &parent->children);
        spin_unlock_irqrestore(&task_group_lock, flags);

        online_fair_sched_group(tg);
}

/* rcu callback to free various structures associated with a task group */
static void sched_free_group_rcu(struct rcu_head *rhp)
{
        /* Now it should be safe to free those cfs_rqs: */
        sched_free_group(container_of(rhp, struct task_group, rcu));
}

void sched_destroy_group(struct task_group *tg)
{
        /* Wait for possible concurrent references to cfs_rqs complete: */
        call_rcu(&tg->rcu, sched_free_group_rcu);
}

void sched_offline_group(struct task_group *tg)
{
        unsigned long flags;

        /* End participation in shares distribution: */
        unregister_fair_sched_group(tg);

        spin_lock_irqsave(&task_group_lock, flags);
        list_del_rcu(&tg->list);
        list_del_rcu(&tg->siblings);
        spin_unlock_irqrestore(&task_group_lock, flags);
}

static void sched_change_group(struct task_struct *tsk, int type)
{
        struct task_group *tg;

        /*
         * All callers are synchronized by task_rq_lock(); we do not use RCU
         * which is pointless here. Thus, we pass "true" to task_css_check()
         * to prevent lockdep warnings.
         */
        tg = container_of(task_css_check(tsk, cpu_cgrp_id, true),
                          struct task_group, css);
        tg = autogroup_task_group(tsk, tg);
        tsk->sched_task_group = tg;

#ifdef CONFIG_FAIR_GROUP_SCHED
        if (tsk->sched_class->task_change_group)
                tsk->sched_class->task_change_group(tsk, type);
        else
#endif
                set_task_rq(tsk, task_cpu(tsk));
}

/*
 * Change task's runqueue when it moves between groups.
 *
 * The caller of this function should have put the task in its new group by
 * now. This function just updates tsk->se.cfs_rq and tsk->se.parent to reflect
 * its new group.
 */
void sched_move_task(struct task_struct *tsk)
{
        int queued, running, queue_flags =
                DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
        struct rq_flags rf;
        struct rq *rq;

        rq = task_rq_lock(tsk, &rf);
        update_rq_clock(rq);

        running = task_current(rq, tsk);
        queued = task_on_rq_queued(tsk);

        if (queued)
                dequeue_task(rq, tsk, queue_flags);
        if (running)
                put_prev_task(rq, tsk);

        sched_change_group(tsk, TASK_MOVE_GROUP);

        if (queued)
                enqueue_task(rq, tsk, queue_flags);
        if (running) {
                set_next_task(rq, tsk);
                /*
                 * After changing group, the running task may have joined a
                 * throttled one but it's still the running task. Trigger a
                 * resched to make sure that task can still run.
                 */
                resched_curr(rq);
        }

        task_rq_unlock(rq, tsk, &rf);
}

static inline struct task_group *css_tg(struct cgroup_subsys_state *css)
{
        return css ? container_of(css, struct task_group, css) : NULL;
}

static struct cgroup_subsys_state *
cpu_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
{
        struct task_group *parent = css_tg(parent_css);
        struct task_group *tg;

        if (!parent) {
                /* This is early initialization for the top cgroup */
                return &root_task_group.css;
        }

        tg = sched_create_group(parent);
        if (IS_ERR(tg))
                return ERR_PTR(-ENOMEM);

        return &tg->css;
}

/* Expose task group only after completing cgroup initialization */
static int cpu_cgroup_css_online(struct cgroup_subsys_state *css)
{
        struct task_group *tg = css_tg(css);
        struct task_group *parent = css_tg(css->parent);

        if (parent)
                sched_online_group(tg, parent);

#ifdef CONFIG_UCLAMP_TASK_GROUP
        /* Propagate the effective uclamp value for the new group */
        cpu_util_update_eff(css);
#endif

        return 0;
}

static void cpu_cgroup_css_released(struct cgroup_subsys_state *css)
{
        struct task_group *tg = css_tg(css);

        sched_offline_group(tg);
}

static void cpu_cgroup_css_free(struct cgroup_subsys_state *css)
{
        struct task_group *tg = css_tg(css);

        /*
         * Relies on the RCU grace period between css_released() and this.
         */
        sched_free_group(tg);
}

/*
 * This is called before wake_up_new_task(), therefore we really only
 * have to set its group bits, all the other stuff does not apply.
 */
static void cpu_cgroup_fork(struct task_struct *task)
{
        struct rq_flags rf;
        struct rq *rq;

        rq = task_rq_lock(task, &rf);

        update_rq_clock(rq);
        sched_change_group(task, TASK_SET_GROUP);

        task_rq_unlock(rq, task, &rf);
}

static int cpu_cgroup_can_attach(struct cgroup_taskset *tset)
{
        struct task_struct *task;
        struct cgroup_subsys_state *css;
        int ret = 0;

        cgroup_taskset_for_each(task, css, tset) {
#ifdef CONFIG_RT_GROUP_SCHED
                if (!sched_rt_can_attach(css_tg(css), task))
                        return -EINVAL;
#endif
                /*
                 * Serialize against wake_up_new_task() such that if its
                 * running, we're sure to observe its full state.
                 */
                raw_spin_lock_irq(&task->pi_lock);
                /*
                 * Avoid calling sched_move_task() before wake_up_new_task()
                 * has happened. This would lead to problems with PELT, due to
                 * move wanting to detach+attach while we're not attached yet.
                 */
                if (task->state == TASK_NEW)
                        ret = -EINVAL;
                raw_spin_unlock_irq(&task->pi_lock);

                if (ret)
                        break;
        }
        return ret;
}

static void cpu_cgroup_attach(struct cgroup_taskset *tset)
{
        struct task_struct *task;
        struct cgroup_subsys_state *css;

        cgroup_taskset_for_each(task, css, tset)
                sched_move_task(task);
}

#ifdef CONFIG_UCLAMP_TASK_GROUP
static void cpu_util_update_eff(struct cgroup_subsys_state *css)
{
        struct cgroup_subsys_state *top_css = css;
        struct uclamp_se *uc_parent = NULL;
        struct uclamp_se *uc_se = NULL;
        unsigned int eff[UCLAMP_CNT];
        enum uclamp_id clamp_id;
        unsigned int clamps;

        css_for_each_descendant_pre(css, top_css) {
                uc_parent = css_tg(css)->parent
                        ? css_tg(css)->parent->uclamp : NULL;

                for_each_clamp_id(clamp_id) {
                        /* Assume effective clamps matches requested clamps */
                        eff[clamp_id] = css_tg(css)->uclamp_req[clamp_id].value;
                        /* Cap effective clamps with parent's effective clamps */
                        if (uc_parent &&
                            eff[clamp_id] > uc_parent[clamp_id].value) {
                                eff[clamp_id] = uc_parent[clamp_id].value;
                        }
                }
                /* Ensure protection is always capped by limit */
                eff[UCLAMP_MIN] = min(eff[UCLAMP_MIN], eff[UCLAMP_MAX]);

                /* Propagate most restrictive effective clamps */
                clamps = 0x0;
                uc_se = css_tg(css)->uclamp;
                for_each_clamp_id(clamp_id) {
                        if (eff[clamp_id] == uc_se[clamp_id].value)
                                continue;
                        uc_se[clamp_id].value = eff[clamp_id];
                        uc_se[clamp_id].bucket_id = uclamp_bucket_id(eff[clamp_id]);
                        clamps |= (0x1 << clamp_id);
                }
                if (!clamps) {
                        css = css_rightmost_descendant(css);
                        continue;
                }

                /* Immediately update descendants RUNNABLE tasks */
                uclamp_update_active_tasks(css, clamps);
        }
}

/*
 * Integer 10^N with a given N exponent by casting to integer the literal "1eN"
 * C expression. Since there is no way to convert a macro argument (N) into a
 * character constant, use two levels of macros.
 */
#define _POW10(exp) ((unsigned int)1e##exp)
#define POW10(exp) _POW10(exp)

struct uclamp_request {
#define UCLAMP_PERCENT_SHIFT    2
#define UCLAMP_PERCENT_SCALE    (100 * POW10(UCLAMP_PERCENT_SHIFT))
        s64 percent;
        u64 util;
        int ret;
};

static inline struct uclamp_request
capacity_from_percent(char *buf)
{
        struct uclamp_request req = {
                .percent = UCLAMP_PERCENT_SCALE,
                .util = SCHED_CAPACITY_SCALE,
                .ret = 0,
        };

        buf = strim(buf);
        if (strcmp(buf, "max")) {
                req.ret = cgroup_parse_float(buf, UCLAMP_PERCENT_SHIFT,
                                             &req.percent);
                if (req.ret)
                        return req;
                if ((u64)req.percent > UCLAMP_PERCENT_SCALE) {
                        req.ret = -ERANGE;
                        return req;
                }

                req.util = req.percent << SCHED_CAPACITY_SHIFT;
                req.util = DIV_ROUND_CLOSEST_ULL(req.util, UCLAMP_PERCENT_SCALE);
        }

        return req;
}

static ssize_t cpu_uclamp_write(struct kernfs_open_file *of, char *buf,
                                size_t nbytes, loff_t off,
                                enum uclamp_id clamp_id)
{
        struct uclamp_request req;
        struct task_group *tg;

        req = capacity_from_percent(buf);
        if (req.ret)
                return req.ret;

        mutex_lock(&uclamp_mutex);
        rcu_read_lock();

        tg = css_tg(of_css(of));
        if (tg->uclamp_req[clamp_id].value != req.util)
                uclamp_se_set(&tg->uclamp_req[clamp_id], req.util, false);

        /*
         * Because of not recoverable conversion rounding we keep track of the
         * exact requested value
         */
        tg->uclamp_pct[clamp_id] = req.percent;

        /* Update effective clamps to track the most restrictive value */
        cpu_util_update_eff(of_css(of));

        rcu_read_unlock();
        mutex_unlock(&uclamp_mutex);

        return nbytes;
}

static ssize_t cpu_uclamp_min_write(struct kernfs_open_file *of,
                                    char *buf, size_t nbytes,
                                    loff_t off)
{
        return cpu_uclamp_write(of, buf, nbytes, off, UCLAMP_MIN);
}

static ssize_t cpu_uclamp_max_write(struct kernfs_open_file *of,
                                    char *buf, size_t nbytes,
                                    loff_t off)
{
        return cpu_uclamp_write(of, buf, nbytes, off, UCLAMP_MAX);
}

static inline void cpu_uclamp_print(struct seq_file *sf,
                                    enum uclamp_id clamp_id)
{
        struct task_group *tg;
        u64 util_clamp;
        u64 percent;
        u32 rem;

        rcu_read_lock();
        tg = css_tg(seq_css(sf));
        util_clamp = tg->uclamp_req[clamp_id].value;
        rcu_read_unlock();

        if (util_clamp == SCHED_CAPACITY_SCALE) {
                seq_puts(sf, "max\n");
                return;
        }

        percent = tg->uclamp_pct[clamp_id];
        percent = div_u64_rem(percent, POW10(UCLAMP_PERCENT_SHIFT), &rem);
        seq_printf(sf, "%llu.%0*u\n", percent, UCLAMP_PERCENT_SHIFT, rem);
}

static int cpu_uclamp_min_show(struct seq_file *sf, void *v)
{
        cpu_uclamp_print(sf, UCLAMP_MIN);
        return 0;
}

static int cpu_uclamp_max_show(struct seq_file *sf, void *v)
{
        cpu_uclamp_print(sf, UCLAMP_MAX);
        return 0;
}
#endif /* CONFIG_UCLAMP_TASK_GROUP */

#ifdef CONFIG_FAIR_GROUP_SCHED
static int cpu_shares_write_u64(struct cgroup_subsys_state *css,
                                struct cftype *cftype, u64 shareval)
{
        if (shareval > scale_load_down(ULONG_MAX))
                shareval = MAX_SHARES;
        return sched_group_set_shares(css_tg(css), scale_load(shareval));
}

static u64 cpu_shares_read_u64(struct cgroup_subsys_state *css,
                               struct cftype *cft)
{
        struct task_group *tg = css_tg(css);

        return (u64) scale_load_down(tg->shares);
}

#ifdef CONFIG_CFS_BANDWIDTH
static DEFINE_MUTEX(cfs_constraints_mutex);

const u64 max_cfs_quota_period = 1 * NSEC_PER_SEC; /* 1s */
static const u64 min_cfs_quota_period = 1 * NSEC_PER_MSEC; /* 1ms */

static int __cfs_schedulable(struct task_group *tg, u64 period, u64 runtime);

static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota)
{
        int i, ret = 0, runtime_enabled, runtime_was_enabled;
        struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;

        if (tg == &root_task_group)
                return -EINVAL;

        /*
         * Ensure we have at some amount of bandwidth every period.  This is
         * to prevent reaching a state of large arrears when throttled via
         * entity_tick() resulting in prolonged exit starvation.
         */
        if (quota < min_cfs_quota_period || period < min_cfs_quota_period)
                return -EINVAL;

        /*
         * Likewise, bound things on the otherside by preventing insane quota
         * periods.  This also allows us to normalize in computing quota
         * feasibility.
         */
        if (period > max_cfs_quota_period)
                return -EINVAL;

        /*
         * Prevent race between setting of cfs_rq->runtime_enabled and
         * unthrottle_offline_cfs_rqs().
         */
        get_online_cpus();
        mutex_lock(&cfs_constraints_mutex);
        ret = __cfs_schedulable(tg, period, quota);
        if (ret)
                goto out_unlock;

        runtime_enabled = quota != RUNTIME_INF;
        runtime_was_enabled = cfs_b->quota != RUNTIME_INF;
        /*
         * If we need to toggle cfs_bandwidth_used, off->on must occur
         * before making related changes, and on->off must occur afterwards
         */
        if (runtime_enabled && !runtime_was_enabled)
                cfs_bandwidth_usage_inc();
        raw_spin_lock_irq(&cfs_b->lock);
        cfs_b->period = ns_to_ktime(period);
        cfs_b->quota = quota;

        __refill_cfs_bandwidth_runtime(cfs_b);

        /* Restart the period timer (if active) to handle new period expiry: */
        if (runtime_enabled)
                start_cfs_bandwidth(cfs_b);

        raw_spin_unlock_irq(&cfs_b->lock);

        for_each_online_cpu(i) {
                struct cfs_rq *cfs_rq = tg->cfs_rq[i];
                struct rq *rq = cfs_rq->rq;
                struct rq_flags rf;

                rq_lock_irq(rq, &rf);
                cfs_rq->runtime_enabled = runtime_enabled;
                cfs_rq->runtime_remaining = 0;

                if (cfs_rq->throttled)
                        unthrottle_cfs_rq(cfs_rq);
                rq_unlock_irq(rq, &rf);
        }
        if (runtime_was_enabled && !runtime_enabled)
                cfs_bandwidth_usage_dec();
out_unlock:
        mutex_unlock(&cfs_constraints_mutex);
        put_online_cpus();

        return ret;
}

static int tg_set_cfs_quota(struct task_group *tg, long cfs_quota_us)
{
        u64 quota, period;

        period = ktime_to_ns(tg->cfs_bandwidth.period);
        if (cfs_quota_us < 0)
                quota = RUNTIME_INF;
        else if ((u64)cfs_quota_us <= U64_MAX / NSEC_PER_USEC)
                quota = (u64)cfs_quota_us * NSEC_PER_USEC;
        else
                return -EINVAL;

        return tg_set_cfs_bandwidth(tg, period, quota);
}

static long tg_get_cfs_quota(struct task_group *tg)
{
        u64 quota_us;

        if (tg->cfs_bandwidth.quota == RUNTIME_INF)
                return -1;

        quota_us = tg->cfs_bandwidth.quota;
        do_div(quota_us, NSEC_PER_USEC);

        return quota_us;
}

static int tg_set_cfs_period(struct task_group *tg, long cfs_period_us)
{
        u64 quota, period;

        if ((u64)cfs_period_us > U64_MAX / NSEC_PER_USEC)
                return -EINVAL;

        period = (u64)cfs_period_us * NSEC_PER_USEC;
        quota = tg->cfs_bandwidth.quota;

        return tg_set_cfs_bandwidth(tg, period, quota);
}

static long tg_get_cfs_period(struct task_group *tg)
{
        u64 cfs_period_us;

        cfs_period_us = ktime_to_ns(tg->cfs_bandwidth.period);
        do_div(cfs_period_us, NSEC_PER_USEC);

        return cfs_period_us;
}

static s64 cpu_cfs_quota_read_s64(struct cgroup_subsys_state *css,
                                  struct cftype *cft)
{
        return tg_get_cfs_quota(css_tg(css));
}

static int cpu_cfs_quota_write_s64(struct cgroup_subsys_state *css,
                                   struct cftype *cftype, s64 cfs_quota_us)
{
        return tg_set_cfs_quota(css_tg(css), cfs_quota_us);
}

static u64 cpu_cfs_period_read_u64(struct cgroup_subsys_state *css,
                                   struct cftype *cft)
{
        return tg_get_cfs_period(css_tg(css));
}

static int cpu_cfs_period_write_u64(struct cgroup_subsys_state *css,
                                    struct cftype *cftype, u64 cfs_period_us)
{
        return tg_set_cfs_period(css_tg(css), cfs_period_us);
}

struct cfs_schedulable_data {
        struct task_group *tg;
        u64 period, quota;
};

/*
 * normalize group quota/period to be quota/max_period
 * note: units are usecs
 */
static u64 normalize_cfs_quota(struct task_group *tg,
                               struct cfs_schedulable_data *d)
{
        u64 quota, period;

        if (tg == d->tg) {
                period = d->period;
                quota = d->quota;
        } else {
                period = tg_get_cfs_period(tg);
                quota = tg_get_cfs_quota(tg);
        }

        /* note: these should typically be equivalent */
        if (quota == RUNTIME_INF || quota == -1)
                return RUNTIME_INF;

        return to_ratio(period, quota);
}

static int tg_cfs_schedulable_down(struct task_group *tg, void *data)
{
        struct cfs_schedulable_data *d = data;
        struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;
        s64 quota = 0, parent_quota = -1;

        if (!tg->parent) {
                quota = RUNTIME_INF;
        } else {
                struct cfs_bandwidth *parent_b = &tg->parent->cfs_bandwidth;

                quota = normalize_cfs_quota(tg, d);
                parent_quota = parent_b->hierarchical_quota;

                /*
                 * Ensure max(child_quota) <= parent_quota.  On cgroup2,
                 * always take the min.  On cgroup1, only inherit when no
                 * limit is set:
                 */
                if (cgroup_subsys_on_dfl(cpu_cgrp_subsys)) {
                        quota = min(quota, parent_quota);
                } else {
                        if (quota == RUNTIME_INF)
                                quota = parent_quota;
                        else if (parent_quota != RUNTIME_INF && quota > parent_quota)
                                return -EINVAL;
                }
        }
        cfs_b->hierarchical_quota = quota;

        return 0;
}

static int __cfs_schedulable(struct task_group *tg, u64 period, u64 quota)
{
        int ret;
        struct cfs_schedulable_data data = {
                .tg = tg,
                .period = period,
                .quota = quota,
        };

        if (quota != RUNTIME_INF) {
                do_div(data.period, NSEC_PER_USEC);
                do_div(data.quota, NSEC_PER_USEC);
        }

        rcu_read_lock();
        ret = walk_tg_tree(tg_cfs_schedulable_down, tg_nop, &data);
        rcu_read_unlock();

        return ret;
}

static int cpu_cfs_stat_show(struct seq_file *sf, void *v)
{
        struct task_group *tg = css_tg(seq_css(sf));
        struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;

        seq_printf(sf, "nr_periods %d\n", cfs_b->nr_periods);
        seq_printf(sf, "nr_throttled %d\n", cfs_b->nr_throttled);
        seq_printf(sf, "throttled_time %llu\n", cfs_b->throttled_time);

        if (schedstat_enabled() && tg != &root_task_group) {
                u64 ws = 0;
                int i;

                for_each_possible_cpu(i)
                        ws += schedstat_val(tg->se[i]->statistics.wait_sum);

                seq_printf(sf, "wait_sum %llu\n", ws);
        }

        return 0;
}
#endif /* CONFIG_CFS_BANDWIDTH */
#endif /* CONFIG_FAIR_GROUP_SCHED */

#ifdef CONFIG_RT_GROUP_SCHED
static int cpu_rt_runtime_write(struct cgroup_subsys_state *css,
                                struct cftype *cft, s64 val)
{
        return sched_group_set_rt_runtime(css_tg(css), val);
}

static s64 cpu_rt_runtime_read(struct cgroup_subsys_state *css,
                               struct cftype *cft)
{
        return sched_group_rt_runtime(css_tg(css));
}

static int cpu_rt_period_write_uint(struct cgroup_subsys_state *css,
                                    struct cftype *cftype, u64 rt_period_us)
{
        return sched_group_set_rt_period(css_tg(css), rt_period_us);
}

static u64 cpu_rt_period_read_uint(struct cgroup_subsys_state *css,
                                   struct cftype *cft)
{
        return sched_group_rt_period(css_tg(css));
}
#endif /* CONFIG_RT_GROUP_SCHED */

static struct cftype cpu_legacy_files[] = {
#ifdef CONFIG_FAIR_GROUP_SCHED
        {
                .name = "shares",
                .read_u64 = cpu_shares_read_u64,
                .write_u64 = cpu_shares_write_u64,
        },
#endif
#ifdef CONFIG_CFS_BANDWIDTH
        {
                .name = "cfs_quota_us",
                .read_s64 = cpu_cfs_quota_read_s64,
                .write_s64 = cpu_cfs_quota_write_s64,
        },
        {
                .name = "cfs_period_us",
                .read_u64 = cpu_cfs_period_read_u64,
                .write_u64 = cpu_cfs_period_write_u64,
        },
        {
                .name = "stat",
                .seq_show = cpu_cfs_stat_show,
        },
#endif
#ifdef CONFIG_RT_GROUP_SCHED
        {
                .name = "rt_runtime_us",
                .read_s64 = cpu_rt_runtime_read,
                .write_s64 = cpu_rt_runtime_write,
        },
        {
                .name = "rt_period_us",
                .read_u64 = cpu_rt_period_read_uint,
                .write_u64 = cpu_rt_period_write_uint,
        },
#endif
#ifdef CONFIG_UCLAMP_TASK_GROUP
        {
                .name = "uclamp.min",
                .flags = CFTYPE_NOT_ON_ROOT,
                .seq_show = cpu_uclamp_min_show,
                .write = cpu_uclamp_min_write,
        },
        {
                .name = "uclamp.max",
                .flags = CFTYPE_NOT_ON_ROOT,
                .seq_show = cpu_uclamp_max_show,
                .write = cpu_uclamp_max_write,
        },
#endif
        { }     /* Terminate */
};

static int cpu_extra_stat_show(struct seq_file *sf,
                               struct cgroup_subsys_state *css)
{
#ifdef CONFIG_CFS_BANDWIDTH
        {
                struct task_group *tg = css_tg(css);
                struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;
                u64 throttled_usec;

                throttled_usec = cfs_b->throttled_time;
                do_div(throttled_usec, NSEC_PER_USEC);

                seq_printf(sf, "nr_periods %d\n"
                           "nr_throttled %d\n"
                           "throttled_usec %llu\n",
                           cfs_b->nr_periods, cfs_b->nr_throttled,
                           throttled_usec);
        }
#endif
        return 0;
}

#ifdef CONFIG_FAIR_GROUP_SCHED
static u64 cpu_weight_read_u64(struct cgroup_subsys_state *css,
                               struct cftype *cft)
{
        struct task_group *tg = css_tg(css);
        u64 weight = scale_load_down(tg->shares);

        return DIV_ROUND_CLOSEST_ULL(weight * CGROUP_WEIGHT_DFL, 1024);
}

static int cpu_weight_write_u64(struct cgroup_subsys_state *css,
                                struct cftype *cft, u64 weight)
{
        /*
         * cgroup weight knobs should use the common MIN, DFL and MAX
         * values which are 1, 100 and 10000 respectively.  While it loses
         * a bit of range on both ends, it maps pretty well onto the shares
         * value used by scheduler and the round-trip conversions preserve
         * the original value over the entire range.
         */
        if (weight < CGROUP_WEIGHT_MIN || weight > CGROUP_WEIGHT_MAX)
                return -ERANGE;

        weight = DIV_ROUND_CLOSEST_ULL(weight * 1024, CGROUP_WEIGHT_DFL);

        return sched_group_set_shares(css_tg(css), scale_load(weight));
}

static s64 cpu_weight_nice_read_s64(struct cgroup_subsys_state *css,
                                    struct cftype *cft)
{
        unsigned long weight = scale_load_down(css_tg(css)->shares);
        int last_delta = INT_MAX;
        int prio, delta;

        /* find the closest nice value to the current weight */
        for (prio = 0; prio < ARRAY_SIZE(sched_prio_to_weight); prio++) {
                delta = abs(sched_prio_to_weight[prio] - weight);
                if (delta >= last_delta)
                        break;
                last_delta = delta;
        }

        return PRIO_TO_NICE(prio - 1 + MAX_RT_PRIO);
}

static int cpu_weight_nice_write_s64(struct cgroup_subsys_state *css,
                                     struct cftype *cft, s64 nice)
{
        unsigned long weight;
        int idx;

        if (nice < MIN_NICE || nice > MAX_NICE)
                return -ERANGE;

        idx = NICE_TO_PRIO(nice) - MAX_RT_PRIO;
        idx = array_index_nospec(idx, 40);
        weight = sched_prio_to_weight[idx];

        return sched_group_set_shares(css_tg(css), scale_load(weight));
}
#endif

static void __maybe_unused cpu_period_quota_print(struct seq_file *sf,
                                                  long period, long quota)
{
        if (quota < 0)
                seq_puts(sf, "max");
        else
                seq_printf(sf, "%ld", quota);

        seq_printf(sf, " %ld\n", period);
}

/* caller should put the current value in *@periodp before calling */
static int __maybe_unused cpu_period_quota_parse(char *buf,
                                                 u64 *periodp, u64 *quotap)
{
        char tok[21];   /* U64_MAX */

        if (sscanf(buf, "%20s %llu", tok, periodp) < 1)
                return -EINVAL;

        *periodp *= NSEC_PER_USEC;

        if (sscanf(tok, "%llu", quotap))
                *quotap *= NSEC_PER_USEC;
        else if (!strcmp(tok, "max"))
                *quotap = RUNTIME_INF;
        else
                return -EINVAL;

        return 0;
}

#ifdef CONFIG_CFS_BANDWIDTH
static int cpu_max_show(struct seq_file *sf, void *v)
{
        struct task_group *tg = css_tg(seq_css(sf));

        cpu_period_quota_print(sf, tg_get_cfs_period(tg), tg_get_cfs_quota(tg));
        return 0;
}

static ssize_t cpu_max_write(struct kernfs_open_file *of,
                             char *buf, size_t nbytes, loff_t off)
{
        struct task_group *tg = css_tg(of_css(of));
        u64 period = tg_get_cfs_period(tg);
        u64 quota;
        int ret;

        ret = cpu_period_quota_parse(buf, &period, &quota);
        if (!ret)
                ret = tg_set_cfs_bandwidth(tg, period, quota);
        return ret ?: nbytes;
}
#endif

static struct cftype cpu_files[] = {
#ifdef CONFIG_FAIR_GROUP_SCHED
        {
                .name = "weight",
                .flags = CFTYPE_NOT_ON_ROOT,
                .read_u64 = cpu_weight_read_u64,
                .write_u64 = cpu_weight_write_u64,
        },
        {
                .name = "weight.nice",
                .flags = CFTYPE_NOT_ON_ROOT,
                .read_s64 = cpu_weight_nice_read_s64,
                .write_s64 = cpu_weight_nice_write_s64,
        },
#endif
#ifdef CONFIG_CFS_BANDWIDTH
        {
                .name = "max",
                .flags = CFTYPE_NOT_ON_ROOT,
                .seq_show = cpu_max_show,
                .write = cpu_max_write,
        },
#endif
#ifdef CONFIG_UCLAMP_TASK_GROUP
        {
                .name = "uclamp.min",
                .flags = CFTYPE_NOT_ON_ROOT,
                .seq_show = cpu_uclamp_min_show,
                .write = cpu_uclamp_min_write,
        },
        {
                .name = "uclamp.max",
                .flags = CFTYPE_NOT_ON_ROOT,
                .seq_show = cpu_uclamp_max_show,
                .write = cpu_uclamp_max_write,
        },
#endif
        { }     /* terminate */
};

struct cgroup_subsys cpu_cgrp_subsys = {
        .css_alloc      = cpu_cgroup_css_alloc,
        .css_online     = cpu_cgroup_css_online,
        .css_released   = cpu_cgroup_css_released,
        .css_free       = cpu_cgroup_css_free,
        .css_extra_stat_show = cpu_extra_stat_show,
        .fork           = cpu_cgroup_fork,
        .can_attach     = cpu_cgroup_can_attach,
        .attach         = cpu_cgroup_attach,
        .legacy_cftypes = cpu_legacy_files,
        .dfl_cftypes    = cpu_files,
        .early_init     = true,
        .threaded       = true,
};

#endif  /* CONFIG_CGROUP_SCHED */

void dump_cpu_task(int cpu)
{
        pr_info("Task dump for CPU %d:\n", cpu);
        sched_show_task(cpu_curr(cpu));
}

/*
 * Nice levels are multiplicative, with a gentle 10% change for every
 * nice level changed. I.e. when a CPU-bound task goes from nice 0 to
 * nice 1, it will get ~10% less CPU time than another CPU-bound task
 * that remained on nice 0.
 *
 * The "10% effect" is relative and cumulative: from _any_ nice level,
 * if you go up 1 level, it's -10% CPU usage, if you go down 1 level
 * it's +10% CPU usage. (to achieve that we use a multiplier of 1.25.
 * If a task goes up by ~10% and another task goes down by ~10% then
 * the relative distance between them is ~25%.)
 */
const int sched_prio_to_weight[40] = {
 /* -20 */     88761,     71755,     56483,     46273,     36291,
 /* -15 */     29154,     23254,     18705,     14949,     11916,
 /* -10 */      9548,      7620,      6100,      4904,      3906,
 /*  -5 */      3121,      2501,      1991,      1586,      1277,
 /*   0 */      1024,       820,       655,       526,       423,
 /*   5 */       335,       272,       215,       172,       137,
 /*  10 */       110,        87,        70,        56,        45,
 /*  15 */        36,        29,        23,        18,        15,
};

/*
 * Inverse (2^32/x) values of the sched_prio_to_weight[] array, precalculated.
 *
 * In cases where the weight does not change often, we can use the
 * precalculated inverse to speed up arithmetics by turning divisions
 * into multiplications:
 */
const u32 sched_prio_to_wmult[40] = {
 /* -20 */     48388,     59856,     76040,     92818,    118348,
 /* -15 */    147320,    184698,    229616,    287308,    360437,
 /* -10 */    449829,    563644,    704093,    875809,   1099582,
 /*  -5 */   1376151,   1717300,   2157191,   2708050,   3363326,
 /*   0 */   4194304,   5237765,   6557202,   8165337,  10153587,
 /*   5 */  12820798,  15790321,  19976592,  24970740,  31350126,
 /*  10 */  39045157,  49367440,  61356676,  76695844,  95443717,
 /*  15 */ 119304647, 148102320, 186737708, 238609294, 286331153,
};

#undef CREATE_TRACE_POINTS