Linux 6.9-rc1

[linux-2.6-microblaze.git] / kernel / time / posix-cpu-timers.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Implement CPU time clocks for the POSIX clock interface.
 */

#include <linux/sched/signal.h>
#include <linux/sched/cputime.h>
#include <linux/posix-timers.h>
#include <linux/errno.h>
#include <linux/math64.h>
#include <linux/uaccess.h>
#include <linux/kernel_stat.h>
#include <trace/events/timer.h>
#include <linux/tick.h>
#include <linux/workqueue.h>
#include <linux/compat.h>
#include <linux/sched/deadline.h>
#include <linux/task_work.h>

#include "posix-timers.h"

static void posix_cpu_timer_rearm(struct k_itimer *timer);

void posix_cputimers_group_init(struct posix_cputimers *pct, u64 cpu_limit)
{
        posix_cputimers_init(pct);
        if (cpu_limit != RLIM_INFINITY) {
                pct->bases[CPUCLOCK_PROF].nextevt = cpu_limit * NSEC_PER_SEC;
                pct->timers_active = true;
        }
}

/*
 * Called after updating RLIMIT_CPU to run cpu timer and update
 * tsk->signal->posix_cputimers.bases[clock].nextevt expiration cache if
 * necessary. Needs siglock protection since other code may update the
 * expiration cache as well.
 *
 * Returns 0 on success, -ESRCH on failure.  Can fail if the task is exiting and
 * we cannot lock_task_sighand.  Cannot fail if task is current.
 */
int update_rlimit_cpu(struct task_struct *task, unsigned long rlim_new)
{
        u64 nsecs = rlim_new * NSEC_PER_SEC;
        unsigned long irq_fl;

        if (!lock_task_sighand(task, &irq_fl))
                return -ESRCH;
        set_process_cpu_timer(task, CPUCLOCK_PROF, &nsecs, NULL);
        unlock_task_sighand(task, &irq_fl);
        return 0;
}

/*
 * Functions for validating access to tasks.
 */
static struct pid *pid_for_clock(const clockid_t clock, bool gettime)
{
        const bool thread = !!CPUCLOCK_PERTHREAD(clock);
        const pid_t upid = CPUCLOCK_PID(clock);
        struct pid *pid;

        if (CPUCLOCK_WHICH(clock) >= CPUCLOCK_MAX)
                return NULL;

        /*
         * If the encoded PID is 0, then the timer is targeted at current
         * or the process to which current belongs.
         */
        if (upid == 0)
                return thread ? task_pid(current) : task_tgid(current);

        pid = find_vpid(upid);
        if (!pid)
                return NULL;

        if (thread) {
                struct task_struct *tsk = pid_task(pid, PIDTYPE_PID);
                return (tsk && same_thread_group(tsk, current)) ? pid : NULL;
        }

        /*
         * For clock_gettime(PROCESS) allow finding the process by
         * with the pid of the current task.  The code needs the tgid
         * of the process so that pid_task(pid, PIDTYPE_TGID) can be
         * used to find the process.
         */
        if (gettime && (pid == task_pid(current)))
                return task_tgid(current);

        /*
         * For processes require that pid identifies a process.
         */
        return pid_has_task(pid, PIDTYPE_TGID) ? pid : NULL;
}

static inline int validate_clock_permissions(const clockid_t clock)
{
        int ret;

        rcu_read_lock();
        ret = pid_for_clock(clock, false) ? 0 : -EINVAL;
        rcu_read_unlock();

        return ret;
}

static inline enum pid_type clock_pid_type(const clockid_t clock)
{
        return CPUCLOCK_PERTHREAD(clock) ? PIDTYPE_PID : PIDTYPE_TGID;
}

static inline struct task_struct *cpu_timer_task_rcu(struct k_itimer *timer)
{
        return pid_task(timer->it.cpu.pid, clock_pid_type(timer->it_clock));
}

/*
 * Update expiry time from increment, and increase overrun count,
 * given the current clock sample.
 */
static u64 bump_cpu_timer(struct k_itimer *timer, u64 now)
{
        u64 delta, incr, expires = timer->it.cpu.node.expires;
        int i;

        if (!timer->it_interval)
                return expires;

        if (now < expires)
                return expires;

        incr = timer->it_interval;
        delta = now + incr - expires;

        /* Don't use (incr*2 < delta), incr*2 might overflow. */
        for (i = 0; incr < delta - incr; i++)
                incr = incr << 1;

        for (; i >= 0; incr >>= 1, i--) {
                if (delta < incr)
                        continue;

                timer->it.cpu.node.expires += incr;
                timer->it_overrun += 1LL << i;
                delta -= incr;
        }
        return timer->it.cpu.node.expires;
}

/* Check whether all cache entries contain U64_MAX, i.e. eternal expiry time */
static inline bool expiry_cache_is_inactive(const struct posix_cputimers *pct)
{
        return !(~pct->bases[CPUCLOCK_PROF].nextevt |
                 ~pct->bases[CPUCLOCK_VIRT].nextevt |
                 ~pct->bases[CPUCLOCK_SCHED].nextevt);
}

static int
posix_cpu_clock_getres(const clockid_t which_clock, struct timespec64 *tp)
{
        int error = validate_clock_permissions(which_clock);

        if (!error) {
                tp->tv_sec = 0;
                tp->tv_nsec = ((NSEC_PER_SEC + HZ - 1) / HZ);
                if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED) {
                        /*
                         * If sched_clock is using a cycle counter, we
                         * don't have any idea of its true resolution
                         * exported, but it is much more than 1s/HZ.
                         */
                        tp->tv_nsec = 1;
                }
        }
        return error;
}

static int
posix_cpu_clock_set(const clockid_t clock, const struct timespec64 *tp)
{
        int error = validate_clock_permissions(clock);

        /*
         * You can never reset a CPU clock, but we check for other errors
         * in the call before failing with EPERM.
         */
        return error ? : -EPERM;
}

/*
 * Sample a per-thread clock for the given task. clkid is validated.
 */
static u64 cpu_clock_sample(const clockid_t clkid, struct task_struct *p)
{
        u64 utime, stime;

        if (clkid == CPUCLOCK_SCHED)
                return task_sched_runtime(p);

        task_cputime(p, &utime, &stime);

        switch (clkid) {
        case CPUCLOCK_PROF:
                return utime + stime;
        case CPUCLOCK_VIRT:
                return utime;
        default:
                WARN_ON_ONCE(1);
        }
        return 0;
}

static inline void store_samples(u64 *samples, u64 stime, u64 utime, u64 rtime)
{
        samples[CPUCLOCK_PROF] = stime + utime;
        samples[CPUCLOCK_VIRT] = utime;
        samples[CPUCLOCK_SCHED] = rtime;
}

static void task_sample_cputime(struct task_struct *p, u64 *samples)
{
        u64 stime, utime;

        task_cputime(p, &utime, &stime);
        store_samples(samples, stime, utime, p->se.sum_exec_runtime);
}

static void proc_sample_cputime_atomic(struct task_cputime_atomic *at,
                                       u64 *samples)
{
        u64 stime, utime, rtime;

        utime = atomic64_read(&at->utime);
        stime = atomic64_read(&at->stime);
        rtime = atomic64_read(&at->sum_exec_runtime);
        store_samples(samples, stime, utime, rtime);
}

/*
 * Set cputime to sum_cputime if sum_cputime > cputime. Use cmpxchg
 * to avoid race conditions with concurrent updates to cputime.
 */
static inline void __update_gt_cputime(atomic64_t *cputime, u64 sum_cputime)
{
        u64 curr_cputime = atomic64_read(cputime);

        do {
                if (sum_cputime <= curr_cputime)
                        return;
        } while (!atomic64_try_cmpxchg(cputime, &curr_cputime, sum_cputime));
}

static void update_gt_cputime(struct task_cputime_atomic *cputime_atomic,
                              struct task_cputime *sum)
{
        __update_gt_cputime(&cputime_atomic->utime, sum->utime);
        __update_gt_cputime(&cputime_atomic->stime, sum->stime);
        __update_gt_cputime(&cputime_atomic->sum_exec_runtime, sum->sum_exec_runtime);
}

/**
 * thread_group_sample_cputime - Sample cputime for a given task
 * @tsk:        Task for which cputime needs to be started
 * @samples:    Storage for time samples
 *
 * Called from sys_getitimer() to calculate the expiry time of an active
 * timer. That means group cputime accounting is already active. Called
 * with task sighand lock held.
 *
 * Updates @times with an uptodate sample of the thread group cputimes.
 */
void thread_group_sample_cputime(struct task_struct *tsk, u64 *samples)
{
        struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
        struct posix_cputimers *pct = &tsk->signal->posix_cputimers;

        WARN_ON_ONCE(!pct->timers_active);

        proc_sample_cputime_atomic(&cputimer->cputime_atomic, samples);
}

/**
 * thread_group_start_cputime - Start cputime and return a sample
 * @tsk:        Task for which cputime needs to be started
 * @samples:    Storage for time samples
 *
 * The thread group cputime accounting is avoided when there are no posix
 * CPU timers armed. Before starting a timer it's required to check whether
 * the time accounting is active. If not, a full update of the atomic
 * accounting store needs to be done and the accounting enabled.
 *
 * Updates @times with an uptodate sample of the thread group cputimes.
 */
static void thread_group_start_cputime(struct task_struct *tsk, u64 *samples)
{
        struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
        struct posix_cputimers *pct = &tsk->signal->posix_cputimers;

        lockdep_assert_task_sighand_held(tsk);

        /* Check if cputimer isn't running. This is accessed without locking. */
        if (!READ_ONCE(pct->timers_active)) {
                struct task_cputime sum;

                /*
                 * The POSIX timer interface allows for absolute time expiry
                 * values through the TIMER_ABSTIME flag, therefore we have
                 * to synchronize the timer to the clock every time we start it.
                 */
                thread_group_cputime(tsk, &sum);
                update_gt_cputime(&cputimer->cputime_atomic, &sum);

                /*
                 * We're setting timers_active without a lock. Ensure this
                 * only gets written to in one operation. We set it after
                 * update_gt_cputime() as a small optimization, but
                 * barriers are not required because update_gt_cputime()
                 * can handle concurrent updates.
                 */
                WRITE_ONCE(pct->timers_active, true);
        }
        proc_sample_cputime_atomic(&cputimer->cputime_atomic, samples);
}

static void __thread_group_cputime(struct task_struct *tsk, u64 *samples)
{
        struct task_cputime ct;

        thread_group_cputime(tsk, &ct);
        store_samples(samples, ct.stime, ct.utime, ct.sum_exec_runtime);
}

/*
 * Sample a process (thread group) clock for the given task clkid. If the
 * group's cputime accounting is already enabled, read the atomic
 * store. Otherwise a full update is required.  clkid is already validated.
 */
static u64 cpu_clock_sample_group(const clockid_t clkid, struct task_struct *p,
                                  bool start)
{
        struct thread_group_cputimer *cputimer = &p->signal->cputimer;
        struct posix_cputimers *pct = &p->signal->posix_cputimers;
        u64 samples[CPUCLOCK_MAX];

        if (!READ_ONCE(pct->timers_active)) {
                if (start)
                        thread_group_start_cputime(p, samples);
                else
                        __thread_group_cputime(p, samples);
        } else {
                proc_sample_cputime_atomic(&cputimer->cputime_atomic, samples);
        }

        return samples[clkid];
}

static int posix_cpu_clock_get(const clockid_t clock, struct timespec64 *tp)
{
        const clockid_t clkid = CPUCLOCK_WHICH(clock);
        struct task_struct *tsk;
        u64 t;

        rcu_read_lock();
        tsk = pid_task(pid_for_clock(clock, true), clock_pid_type(clock));
        if (!tsk) {
                rcu_read_unlock();
                return -EINVAL;
        }

        if (CPUCLOCK_PERTHREAD(clock))
                t = cpu_clock_sample(clkid, tsk);
        else
                t = cpu_clock_sample_group(clkid, tsk, false);
        rcu_read_unlock();

        *tp = ns_to_timespec64(t);
        return 0;
}

/*
 * Validate the clockid_t for a new CPU-clock timer, and initialize the timer.
 * This is called from sys_timer_create() and do_cpu_nanosleep() with the
 * new timer already all-zeros initialized.
 */
static int posix_cpu_timer_create(struct k_itimer *new_timer)
{
        static struct lock_class_key posix_cpu_timers_key;
        struct pid *pid;

        rcu_read_lock();
        pid = pid_for_clock(new_timer->it_clock, false);
        if (!pid) {
                rcu_read_unlock();
                return -EINVAL;
        }

        /*
         * If posix timer expiry is handled in task work context then
         * timer::it_lock can be taken without disabling interrupts as all
         * other locking happens in task context. This requires a separate
         * lock class key otherwise regular posix timer expiry would record
         * the lock class being taken in interrupt context and generate a
         * false positive warning.
         */
        if (IS_ENABLED(CONFIG_POSIX_CPU_TIMERS_TASK_WORK))
                lockdep_set_class(&new_timer->it_lock, &posix_cpu_timers_key);

        new_timer->kclock = &clock_posix_cpu;
        timerqueue_init(&new_timer->it.cpu.node);
        new_timer->it.cpu.pid = get_pid(pid);
        rcu_read_unlock();
        return 0;
}

static struct posix_cputimer_base *timer_base(struct k_itimer *timer,
                                              struct task_struct *tsk)
{
        int clkidx = CPUCLOCK_WHICH(timer->it_clock);

        if (CPUCLOCK_PERTHREAD(timer->it_clock))
                return tsk->posix_cputimers.bases + clkidx;
        else
                return tsk->signal->posix_cputimers.bases + clkidx;
}

/*
 * Force recalculating the base earliest expiration on the next tick.
 * This will also re-evaluate the need to keep around the process wide
 * cputime counter and tick dependency and eventually shut these down
 * if necessary.
 */
static void trigger_base_recalc_expires(struct k_itimer *timer,
                                        struct task_struct *tsk)
{
        struct posix_cputimer_base *base = timer_base(timer, tsk);

        base->nextevt = 0;
}

/*
 * Dequeue the timer and reset the base if it was its earliest expiration.
 * It makes sure the next tick recalculates the base next expiration so we
 * don't keep the costly process wide cputime counter around for a random
 * amount of time, along with the tick dependency.
 *
 * If another timer gets queued between this and the next tick, its
 * expiration will update the base next event if necessary on the next
 * tick.
 */
static void disarm_timer(struct k_itimer *timer, struct task_struct *p)
{
        struct cpu_timer *ctmr = &timer->it.cpu;
        struct posix_cputimer_base *base;

        if (!cpu_timer_dequeue(ctmr))
                return;

        base = timer_base(timer, p);
        if (cpu_timer_getexpires(ctmr) == base->nextevt)
                trigger_base_recalc_expires(timer, p);
}


/*
 * Clean up a CPU-clock timer that is about to be destroyed.
 * This is called from timer deletion with the timer already locked.
 * If we return TIMER_RETRY, it's necessary to release the timer's lock
 * and try again.  (This happens when the timer is in the middle of firing.)
 */
static int posix_cpu_timer_del(struct k_itimer *timer)
{
        struct cpu_timer *ctmr = &timer->it.cpu;
        struct sighand_struct *sighand;
        struct task_struct *p;
        unsigned long flags;
        int ret = 0;

        rcu_read_lock();
        p = cpu_timer_task_rcu(timer);
        if (!p)
                goto out;

        /*
         * Protect against sighand release/switch in exit/exec and process/
         * thread timer list entry concurrent read/writes.
         */
        sighand = lock_task_sighand(p, &flags);
        if (unlikely(sighand == NULL)) {
                /*
                 * This raced with the reaping of the task. The exit cleanup
                 * should have removed this timer from the timer queue.
                 */
                WARN_ON_ONCE(ctmr->head || timerqueue_node_queued(&ctmr->node));
        } else {
                if (timer->it.cpu.firing)
                        ret = TIMER_RETRY;
                else
                        disarm_timer(timer, p);

                unlock_task_sighand(p, &flags);
        }

out:
        rcu_read_unlock();
        if (!ret)
                put_pid(ctmr->pid);

        return ret;
}

static void cleanup_timerqueue(struct timerqueue_head *head)
{
        struct timerqueue_node *node;
        struct cpu_timer *ctmr;

        while ((node = timerqueue_getnext(head))) {
                timerqueue_del(head, node);
                ctmr = container_of(node, struct cpu_timer, node);
                ctmr->head = NULL;
        }
}

/*
 * Clean out CPU timers which are still armed when a thread exits. The
 * timers are only removed from the list. No other updates are done. The
 * corresponding posix timers are still accessible, but cannot be rearmed.
 *
 * This must be called with the siglock held.
 */
static void cleanup_timers(struct posix_cputimers *pct)
{
        cleanup_timerqueue(&pct->bases[CPUCLOCK_PROF].tqhead);
        cleanup_timerqueue(&pct->bases[CPUCLOCK_VIRT].tqhead);
        cleanup_timerqueue(&pct->bases[CPUCLOCK_SCHED].tqhead);
}

/*
 * These are both called with the siglock held, when the current thread
 * is being reaped.  When the final (leader) thread in the group is reaped,
 * posix_cpu_timers_exit_group will be called after posix_cpu_timers_exit.
 */
void posix_cpu_timers_exit(struct task_struct *tsk)
{
        cleanup_timers(&tsk->posix_cputimers);
}
void posix_cpu_timers_exit_group(struct task_struct *tsk)
{
        cleanup_timers(&tsk->signal->posix_cputimers);
}

/*
 * Insert the timer on the appropriate list before any timers that
 * expire later.  This must be called with the sighand lock held.
 */
static void arm_timer(struct k_itimer *timer, struct task_struct *p)
{
        struct posix_cputimer_base *base = timer_base(timer, p);
        struct cpu_timer *ctmr = &timer->it.cpu;
        u64 newexp = cpu_timer_getexpires(ctmr);

        if (!cpu_timer_enqueue(&base->tqhead, ctmr))
                return;

        /*
         * We are the new earliest-expiring POSIX 1.b timer, hence
         * need to update expiration cache. Take into account that
         * for process timers we share expiration cache with itimers
         * and RLIMIT_CPU and for thread timers with RLIMIT_RTTIME.
         */
        if (newexp < base->nextevt)
                base->nextevt = newexp;

        if (CPUCLOCK_PERTHREAD(timer->it_clock))
                tick_dep_set_task(p, TICK_DEP_BIT_POSIX_TIMER);
        else
                tick_dep_set_signal(p, TICK_DEP_BIT_POSIX_TIMER);
}

/*
 * The timer is locked, fire it and arrange for its reload.
 */
static void cpu_timer_fire(struct k_itimer *timer)
{
        struct cpu_timer *ctmr = &timer->it.cpu;

        if ((timer->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE) {
                /*
                 * User don't want any signal.
                 */
                cpu_timer_setexpires(ctmr, 0);
        } else if (unlikely(timer->sigq == NULL)) {
                /*
                 * This a special case for clock_nanosleep,
                 * not a normal timer from sys_timer_create.
                 */
                wake_up_process(timer->it_process);
                cpu_timer_setexpires(ctmr, 0);
        } else if (!timer->it_interval) {
                /*
                 * One-shot timer.  Clear it as soon as it's fired.
                 */
                posix_timer_event(timer, 0);
                cpu_timer_setexpires(ctmr, 0);
        } else if (posix_timer_event(timer, ++timer->it_requeue_pending)) {
                /*
                 * The signal did not get queued because the signal
                 * was ignored, so we won't get any callback to
                 * reload the timer.  But we need to keep it
                 * ticking in case the signal is deliverable next time.
                 */
                posix_cpu_timer_rearm(timer);
                ++timer->it_requeue_pending;
        }
}

/*
 * Guts of sys_timer_settime for CPU timers.
 * This is called with the timer locked and interrupts disabled.
 * If we return TIMER_RETRY, it's necessary to release the timer's lock
 * and try again.  (This happens when the timer is in the middle of firing.)
 */
static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
                               struct itimerspec64 *new, struct itimerspec64 *old)
{
        clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);
        u64 old_expires, new_expires, old_incr, val;
        struct cpu_timer *ctmr = &timer->it.cpu;
        struct sighand_struct *sighand;
        struct task_struct *p;
        unsigned long flags;
        int ret = 0;

        rcu_read_lock();
        p = cpu_timer_task_rcu(timer);
        if (!p) {
                /*
                 * If p has just been reaped, we can no
                 * longer get any information about it at all.
                 */
                rcu_read_unlock();
                return -ESRCH;
        }

        /*
         * Use the to_ktime conversion because that clamps the maximum
         * value to KTIME_MAX and avoid multiplication overflows.
         */
        new_expires = ktime_to_ns(timespec64_to_ktime(new->it_value));

        /*
         * Protect against sighand release/switch in exit/exec and p->cpu_timers
         * and p->signal->cpu_timers read/write in arm_timer()
         */
        sighand = lock_task_sighand(p, &flags);
        /*
         * If p has just been reaped, we can no
         * longer get any information about it at all.
         */
        if (unlikely(sighand == NULL)) {
                rcu_read_unlock();
                return -ESRCH;
        }

        /*
         * Disarm any old timer after extracting its expiry time.
         */
        old_incr = timer->it_interval;
        old_expires = cpu_timer_getexpires(ctmr);

        if (unlikely(timer->it.cpu.firing)) {
                timer->it.cpu.firing = -1;
                ret = TIMER_RETRY;
        } else {
                cpu_timer_dequeue(ctmr);
        }

        /*
         * We need to sample the current value to convert the new
         * value from to relative and absolute, and to convert the
         * old value from absolute to relative.  To set a process
         * timer, we need a sample to balance the thread expiry
         * times (in arm_timer).  With an absolute time, we must
         * check if it's already passed.  In short, we need a sample.
         */
        if (CPUCLOCK_PERTHREAD(timer->it_clock))
                val = cpu_clock_sample(clkid, p);
        else
                val = cpu_clock_sample_group(clkid, p, true);

        if (old) {
                if (old_expires == 0) {
                        old->it_value.tv_sec = 0;
                        old->it_value.tv_nsec = 0;
                } else {
                        /*
                         * Update the timer in case it has overrun already.
                         * If it has, we'll report it as having overrun and
                         * with the next reloaded timer already ticking,
                         * though we are swallowing that pending
                         * notification here to install the new setting.
                         */
                        u64 exp = bump_cpu_timer(timer, val);

                        if (val < exp) {
                                old_expires = exp - val;
                                old->it_value = ns_to_timespec64(old_expires);
                        } else {
                                old->it_value.tv_nsec = 1;
                                old->it_value.tv_sec = 0;
                        }
                }
        }

        if (unlikely(ret)) {
                /*
                 * We are colliding with the timer actually firing.
                 * Punt after filling in the timer's old value, and
                 * disable this firing since we are already reporting
                 * it as an overrun (thanks to bump_cpu_timer above).
                 */
                unlock_task_sighand(p, &flags);
                goto out;
        }

        if (new_expires != 0 && !(timer_flags & TIMER_ABSTIME)) {
                new_expires += val;
        }

        /*
         * Install the new expiry time (or zero).
         * For a timer with no notification action, we don't actually
         * arm the timer (we'll just fake it for timer_gettime).
         */
        cpu_timer_setexpires(ctmr, new_expires);
        if (new_expires != 0 && val < new_expires) {
                arm_timer(timer, p);
        }

        unlock_task_sighand(p, &flags);
        /*
         * Install the new reload setting, and
         * set up the signal and overrun bookkeeping.
         */
        timer->it_interval = timespec64_to_ktime(new->it_interval);

        /*
         * This acts as a modification timestamp for the timer,
         * so any automatic reload attempt will punt on seeing
         * that we have reset the timer manually.
         */
        timer->it_requeue_pending = (timer->it_requeue_pending + 2) &
                ~REQUEUE_PENDING;
        timer->it_overrun_last = 0;
        timer->it_overrun = -1;

        if (val >= new_expires) {
                if (new_expires != 0) {
                        /*
                         * The designated time already passed, so we notify
                         * immediately, even if the thread never runs to
                         * accumulate more time on this clock.
                         */
                        cpu_timer_fire(timer);
                }

                /*
                 * Make sure we don't keep around the process wide cputime
                 * counter or the tick dependency if they are not necessary.
                 */
                sighand = lock_task_sighand(p, &flags);
                if (!sighand)
                        goto out;

                if (!cpu_timer_queued(ctmr))
                        trigger_base_recalc_expires(timer, p);

                unlock_task_sighand(p, &flags);
        }
 out:
        rcu_read_unlock();
        if (old)
                old->it_interval = ns_to_timespec64(old_incr);

        return ret;
}

static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp)
{
        clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);
        struct cpu_timer *ctmr = &timer->it.cpu;
        u64 now, expires = cpu_timer_getexpires(ctmr);
        struct task_struct *p;

        rcu_read_lock();
        p = cpu_timer_task_rcu(timer);
        if (!p)
                goto out;

        /*
         * Easy part: convert the reload time.
         */
        itp->it_interval = ktime_to_timespec64(timer->it_interval);

        if (!expires)
                goto out;

        /*
         * Sample the clock to take the difference with the expiry time.
         */
        if (CPUCLOCK_PERTHREAD(timer->it_clock))
                now = cpu_clock_sample(clkid, p);
        else
                now = cpu_clock_sample_group(clkid, p, false);

        if (now < expires) {
                itp->it_value = ns_to_timespec64(expires - now);
        } else {
                /*
                 * The timer should have expired already, but the firing
                 * hasn't taken place yet.  Say it's just about to expire.
                 */
                itp->it_value.tv_nsec = 1;
                itp->it_value.tv_sec = 0;
        }
out:
        rcu_read_unlock();
}

#define MAX_COLLECTED   20

static u64 collect_timerqueue(struct timerqueue_head *head,
                              struct list_head *firing, u64 now)
{
        struct timerqueue_node *next;
        int i = 0;

        while ((next = timerqueue_getnext(head))) {
                struct cpu_timer *ctmr;
                u64 expires;

                ctmr = container_of(next, struct cpu_timer, node);
                expires = cpu_timer_getexpires(ctmr);
                /* Limit the number of timers to expire at once */
                if (++i == MAX_COLLECTED || now < expires)
                        return expires;

                ctmr->firing = 1;
                /* See posix_cpu_timer_wait_running() */
                rcu_assign_pointer(ctmr->handling, current);
                cpu_timer_dequeue(ctmr);
                list_add_tail(&ctmr->elist, firing);
        }

        return U64_MAX;
}

static void collect_posix_cputimers(struct posix_cputimers *pct, u64 *samples,
                                    struct list_head *firing)
{
        struct posix_cputimer_base *base = pct->bases;
        int i;

        for (i = 0; i < CPUCLOCK_MAX; i++, base++) {
                base->nextevt = collect_timerqueue(&base->tqhead, firing,
                                                    samples[i]);
        }
}

static inline void check_dl_overrun(struct task_struct *tsk)
{
        if (tsk->dl.dl_overrun) {
                tsk->dl.dl_overrun = 0;
                send_signal_locked(SIGXCPU, SEND_SIG_PRIV, tsk, PIDTYPE_TGID);
        }
}

static bool check_rlimit(u64 time, u64 limit, int signo, bool rt, bool hard)
{
        if (time < limit)
                return false;

        if (print_fatal_signals) {
                pr_info("%s Watchdog Timeout (%s): %s[%d]\n",
                        rt ? "RT" : "CPU", hard ? "hard" : "soft",
                        current->comm, task_pid_nr(current));
        }
        send_signal_locked(signo, SEND_SIG_PRIV, current, PIDTYPE_TGID);
        return true;
}

/*
 * Check for any per-thread CPU timers that have fired and move them off
 * the tsk->cpu_timers[N] list onto the firing list.  Here we update the
 * tsk->it_*_expires values to reflect the remaining thread CPU timers.
 */
static void check_thread_timers(struct task_struct *tsk,
                                struct list_head *firing)
{
        struct posix_cputimers *pct = &tsk->posix_cputimers;
        u64 samples[CPUCLOCK_MAX];
        unsigned long soft;

        if (dl_task(tsk))
                check_dl_overrun(tsk);

        if (expiry_cache_is_inactive(pct))
                return;

        task_sample_cputime(tsk, samples);
        collect_posix_cputimers(pct, samples, firing);

        /*
         * Check for the special case thread timers.
         */
        soft = task_rlimit(tsk, RLIMIT_RTTIME);
        if (soft != RLIM_INFINITY) {
                /* Task RT timeout is accounted in jiffies. RTTIME is usec */
                unsigned long rttime = tsk->rt.timeout * (USEC_PER_SEC / HZ);
                unsigned long hard = task_rlimit_max(tsk, RLIMIT_RTTIME);

                /* At the hard limit, send SIGKILL. No further action. */
                if (hard != RLIM_INFINITY &&
                    check_rlimit(rttime, hard, SIGKILL, true, true))
                        return;

                /* At the soft limit, send a SIGXCPU every second */
                if (check_rlimit(rttime, soft, SIGXCPU, true, false)) {
                        soft += USEC_PER_SEC;
                        tsk->signal->rlim[RLIMIT_RTTIME].rlim_cur = soft;
                }
        }

        if (expiry_cache_is_inactive(pct))
                tick_dep_clear_task(tsk, TICK_DEP_BIT_POSIX_TIMER);
}

static inline void stop_process_timers(struct signal_struct *sig)
{
        struct posix_cputimers *pct = &sig->posix_cputimers;

        /* Turn off the active flag. This is done without locking. */
        WRITE_ONCE(pct->timers_active, false);
        tick_dep_clear_signal(sig, TICK_DEP_BIT_POSIX_TIMER);
}

static void check_cpu_itimer(struct task_struct *tsk, struct cpu_itimer *it,
                             u64 *expires, u64 cur_time, int signo)
{
        if (!it->expires)
                return;

        if (cur_time >= it->expires) {
                if (it->incr)
                        it->expires += it->incr;
                else
                        it->expires = 0;

                trace_itimer_expire(signo == SIGPROF ?
                                    ITIMER_PROF : ITIMER_VIRTUAL,
                                    task_tgid(tsk), cur_time);
                send_signal_locked(signo, SEND_SIG_PRIV, tsk, PIDTYPE_TGID);
        }

        if (it->expires && it->expires < *expires)
                *expires = it->expires;
}

/*
 * Check for any per-thread CPU timers that have fired and move them
 * off the tsk->*_timers list onto the firing list.  Per-thread timers
 * have already been taken off.
 */
static void check_process_timers(struct task_struct *tsk,
                                 struct list_head *firing)
{
        struct signal_struct *const sig = tsk->signal;
        struct posix_cputimers *pct = &sig->posix_cputimers;
        u64 samples[CPUCLOCK_MAX];
        unsigned long soft;

        /*
         * If there are no active process wide timers (POSIX 1.b, itimers,
         * RLIMIT_CPU) nothing to check. Also skip the process wide timer
         * processing when there is already another task handling them.
         */
        if (!READ_ONCE(pct->timers_active) || pct->expiry_active)
                return;

        /*
         * Signify that a thread is checking for process timers.
         * Write access to this field is protected by the sighand lock.
         */
        pct->expiry_active = true;

        /*
         * Collect the current process totals. Group accounting is active
         * so the sample can be taken directly.
         */
        proc_sample_cputime_atomic(&sig->cputimer.cputime_atomic, samples);
        collect_posix_cputimers(pct, samples, firing);

        /*
         * Check for the special case process timers.
         */
        check_cpu_itimer(tsk, &sig->it[CPUCLOCK_PROF],
                         &pct->bases[CPUCLOCK_PROF].nextevt,
                         samples[CPUCLOCK_PROF], SIGPROF);
        check_cpu_itimer(tsk, &sig->it[CPUCLOCK_VIRT],
                         &pct->bases[CPUCLOCK_VIRT].nextevt,
                         samples[CPUCLOCK_VIRT], SIGVTALRM);

        soft = task_rlimit(tsk, RLIMIT_CPU);
        if (soft != RLIM_INFINITY) {
                /* RLIMIT_CPU is in seconds. Samples are nanoseconds */
                unsigned long hard = task_rlimit_max(tsk, RLIMIT_CPU);
                u64 ptime = samples[CPUCLOCK_PROF];
                u64 softns = (u64)soft * NSEC_PER_SEC;
                u64 hardns = (u64)hard * NSEC_PER_SEC;

                /* At the hard limit, send SIGKILL. No further action. */
                if (hard != RLIM_INFINITY &&
                    check_rlimit(ptime, hardns, SIGKILL, false, true))
                        return;

                /* At the soft limit, send a SIGXCPU every second */
                if (check_rlimit(ptime, softns, SIGXCPU, false, false)) {
                        sig->rlim[RLIMIT_CPU].rlim_cur = soft + 1;
                        softns += NSEC_PER_SEC;
                }

                /* Update the expiry cache */
                if (softns < pct->bases[CPUCLOCK_PROF].nextevt)
                        pct->bases[CPUCLOCK_PROF].nextevt = softns;
        }

        if (expiry_cache_is_inactive(pct))
                stop_process_timers(sig);

        pct->expiry_active = false;
}

/*
 * This is called from the signal code (via posixtimer_rearm)
 * when the last timer signal was delivered and we have to reload the timer.
 */
static void posix_cpu_timer_rearm(struct k_itimer *timer)
{
        clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);
        struct task_struct *p;
        struct sighand_struct *sighand;
        unsigned long flags;
        u64 now;

        rcu_read_lock();
        p = cpu_timer_task_rcu(timer);
        if (!p)
                goto out;

        /* Protect timer list r/w in arm_timer() */
        sighand = lock_task_sighand(p, &flags);
        if (unlikely(sighand == NULL))
                goto out;

        /*
         * Fetch the current sample and update the timer's expiry time.
         */
        if (CPUCLOCK_PERTHREAD(timer->it_clock))
                now = cpu_clock_sample(clkid, p);
        else
                now = cpu_clock_sample_group(clkid, p, true);

        bump_cpu_timer(timer, now);

        /*
         * Now re-arm for the new expiry time.
         */
        arm_timer(timer, p);
        unlock_task_sighand(p, &flags);
out:
        rcu_read_unlock();
}

/**
 * task_cputimers_expired - Check whether posix CPU timers are expired
 *
 * @samples:    Array of current samples for the CPUCLOCK clocks
 * @pct:        Pointer to a posix_cputimers container
 *
 * Returns true if any member of @samples is greater than the corresponding
 * member of @pct->bases[CLK].nextevt. False otherwise
 */
static inline bool
task_cputimers_expired(const u64 *samples, struct posix_cputimers *pct)
{
        int i;

        for (i = 0; i < CPUCLOCK_MAX; i++) {
                if (samples[i] >= pct->bases[i].nextevt)
                        return true;
        }
        return false;
}

/**
 * fastpath_timer_check - POSIX CPU timers fast path.
 *
 * @tsk:        The task (thread) being checked.
 *
 * Check the task and thread group timers.  If both are zero (there are no
 * timers set) return false.  Otherwise snapshot the task and thread group
 * timers and compare them with the corresponding expiration times.  Return
 * true if a timer has expired, else return false.
 */
static inline bool fastpath_timer_check(struct task_struct *tsk)
{
        struct posix_cputimers *pct = &tsk->posix_cputimers;
        struct signal_struct *sig;

        if (!expiry_cache_is_inactive(pct)) {
                u64 samples[CPUCLOCK_MAX];

                task_sample_cputime(tsk, samples);
                if (task_cputimers_expired(samples, pct))
                        return true;
        }

        sig = tsk->signal;
        pct = &sig->posix_cputimers;
        /*
         * Check if thread group timers expired when timers are active and
         * no other thread in the group is already handling expiry for
         * thread group cputimers. These fields are read without the
         * sighand lock. However, this is fine because this is meant to be
         * a fastpath heuristic to determine whether we should try to
         * acquire the sighand lock to handle timer expiry.
         *
         * In the worst case scenario, if concurrently timers_active is set
         * or expiry_active is cleared, but the current thread doesn't see
         * the change yet, the timer checks are delayed until the next
         * thread in the group gets a scheduler interrupt to handle the
         * timer. This isn't an issue in practice because these types of
         * delays with signals actually getting sent are expected.
         */
        if (READ_ONCE(pct->timers_active) && !READ_ONCE(pct->expiry_active)) {
                u64 samples[CPUCLOCK_MAX];

                proc_sample_cputime_atomic(&sig->cputimer.cputime_atomic,
                                           samples);

                if (task_cputimers_expired(samples, pct))
                        return true;
        }

        if (dl_task(tsk) && tsk->dl.dl_overrun)
                return true;

        return false;
}

static void handle_posix_cpu_timers(struct task_struct *tsk);

#ifdef CONFIG_POSIX_CPU_TIMERS_TASK_WORK
static void posix_cpu_timers_work(struct callback_head *work)
{
        struct posix_cputimers_work *cw = container_of(work, typeof(*cw), work);

        mutex_lock(&cw->mutex);
        handle_posix_cpu_timers(current);
        mutex_unlock(&cw->mutex);
}

/*
 * Invoked from the posix-timer core when a cancel operation failed because
 * the timer is marked firing. The caller holds rcu_read_lock(), which
 * protects the timer and the task which is expiring it from being freed.
 */
static void posix_cpu_timer_wait_running(struct k_itimer *timr)
{
        struct task_struct *tsk = rcu_dereference(timr->it.cpu.handling);

        /* Has the handling task completed expiry already? */
        if (!tsk)
                return;

        /* Ensure that the task cannot go away */
        get_task_struct(tsk);
        /* Now drop the RCU protection so the mutex can be locked */
        rcu_read_unlock();
        /* Wait on the expiry mutex */
        mutex_lock(&tsk->posix_cputimers_work.mutex);
        /* Release it immediately again. */
        mutex_unlock(&tsk->posix_cputimers_work.mutex);
        /* Drop the task reference. */
        put_task_struct(tsk);
        /* Relock RCU so the callsite is balanced */
        rcu_read_lock();
}

static void posix_cpu_timer_wait_running_nsleep(struct k_itimer *timr)
{
        /* Ensure that timr->it.cpu.handling task cannot go away */
        rcu_read_lock();
        spin_unlock_irq(&timr->it_lock);
        posix_cpu_timer_wait_running(timr);
        rcu_read_unlock();
        /* @timr is on stack and is valid */
        spin_lock_irq(&timr->it_lock);
}

/*
 * Clear existing posix CPU timers task work.
 */
void clear_posix_cputimers_work(struct task_struct *p)
{
        /*
         * A copied work entry from the old task is not meaningful, clear it.
         * N.B. init_task_work will not do this.
         */
        memset(&p->posix_cputimers_work.work, 0,
               sizeof(p->posix_cputimers_work.work));
        init_task_work(&p->posix_cputimers_work.work,
                       posix_cpu_timers_work);
        mutex_init(&p->posix_cputimers_work.mutex);
        p->posix_cputimers_work.scheduled = false;
}

/*
 * Initialize posix CPU timers task work in init task. Out of line to
 * keep the callback static and to avoid header recursion hell.
 */
void __init posix_cputimers_init_work(void)
{
        clear_posix_cputimers_work(current);
}

/*
 * Note: All operations on tsk->posix_cputimer_work.scheduled happen either
 * in hard interrupt context or in task context with interrupts
 * disabled. Aside of that the writer/reader interaction is always in the
 * context of the current task, which means they are strict per CPU.
 */
static inline bool posix_cpu_timers_work_scheduled(struct task_struct *tsk)
{
        return tsk->posix_cputimers_work.scheduled;
}

static inline void __run_posix_cpu_timers(struct task_struct *tsk)
{
        if (WARN_ON_ONCE(tsk->posix_cputimers_work.scheduled))
                return;

        /* Schedule task work to actually expire the timers */
        tsk->posix_cputimers_work.scheduled = true;
        task_work_add(tsk, &tsk->posix_cputimers_work.work, TWA_RESUME);
}

static inline bool posix_cpu_timers_enable_work(struct task_struct *tsk,
                                                unsigned long start)
{
        bool ret = true;

        /*
         * On !RT kernels interrupts are disabled while collecting expired
         * timers, so no tick can happen and the fast path check can be
         * reenabled without further checks.
         */
        if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
                tsk->posix_cputimers_work.scheduled = false;
                return true;
        }

        /*
         * On RT enabled kernels ticks can happen while the expired timers
         * are collected under sighand lock. But any tick which observes
         * the CPUTIMERS_WORK_SCHEDULED bit set, does not run the fastpath
         * checks. So reenabling the tick work has do be done carefully:
         *
         * Disable interrupts and run the fast path check if jiffies have
         * advanced since the collecting of expired timers started. If
         * jiffies have not advanced or the fast path check did not find
         * newly expired timers, reenable the fast path check in the timer
         * interrupt. If there are newly expired timers, return false and
         * let the collection loop repeat.
         */
        local_irq_disable();
        if (start != jiffies && fastpath_timer_check(tsk))
                ret = false;
        else
                tsk->posix_cputimers_work.scheduled = false;
        local_irq_enable();

        return ret;
}
#else /* CONFIG_POSIX_CPU_TIMERS_TASK_WORK */
static inline void __run_posix_cpu_timers(struct task_struct *tsk)
{
        lockdep_posixtimer_enter();
        handle_posix_cpu_timers(tsk);
        lockdep_posixtimer_exit();
}

static void posix_cpu_timer_wait_running(struct k_itimer *timr)
{
        cpu_relax();
}

static void posix_cpu_timer_wait_running_nsleep(struct k_itimer *timr)
{
        spin_unlock_irq(&timr->it_lock);
        cpu_relax();
        spin_lock_irq(&timr->it_lock);
}

static inline bool posix_cpu_timers_work_scheduled(struct task_struct *tsk)
{
        return false;
}

static inline bool posix_cpu_timers_enable_work(struct task_struct *tsk,
                                                unsigned long start)
{
        return true;
}
#endif /* CONFIG_POSIX_CPU_TIMERS_TASK_WORK */

static void handle_posix_cpu_timers(struct task_struct *tsk)
{
        struct k_itimer *timer, *next;
        unsigned long flags, start;
        LIST_HEAD(firing);

        if (!lock_task_sighand(tsk, &flags))
                return;

        do {
                /*
                 * On RT locking sighand lock does not disable interrupts,
                 * so this needs to be careful vs. ticks. Store the current
                 * jiffies value.
                 */
                start = READ_ONCE(jiffies);
                barrier();

                /*
                 * Here we take off tsk->signal->cpu_timers[N] and
                 * tsk->cpu_timers[N] all the timers that are firing, and
                 * put them on the firing list.
                 */
                check_thread_timers(tsk, &firing);

                check_process_timers(tsk, &firing);

                /*
                 * The above timer checks have updated the expiry cache and
                 * because nothing can have queued or modified timers after
                 * sighand lock was taken above it is guaranteed to be
                 * consistent. So the next timer interrupt fastpath check
                 * will find valid data.
                 *
                 * If timer expiry runs in the timer interrupt context then
                 * the loop is not relevant as timers will be directly
                 * expired in interrupt context. The stub function below
                 * returns always true which allows the compiler to
                 * optimize the loop out.
                 *
                 * If timer expiry is deferred to task work context then
                 * the following rules apply:
                 *
                 * - On !RT kernels no tick can have happened on this CPU
                 *   after sighand lock was acquired because interrupts are
                 *   disabled. So reenabling task work before dropping
                 *   sighand lock and reenabling interrupts is race free.
                 *
                 * - On RT kernels ticks might have happened but the tick
                 *   work ignored posix CPU timer handling because the
                 *   CPUTIMERS_WORK_SCHEDULED bit is set. Reenabling work
                 *   must be done very carefully including a check whether
                 *   ticks have happened since the start of the timer
                 *   expiry checks. posix_cpu_timers_enable_work() takes
                 *   care of that and eventually lets the expiry checks
                 *   run again.
                 */
        } while (!posix_cpu_timers_enable_work(tsk, start));

        /*
         * We must release sighand lock before taking any timer's lock.
         * There is a potential race with timer deletion here, as the
         * siglock now protects our private firing list.  We have set
         * the firing flag in each timer, so that a deletion attempt
         * that gets the timer lock before we do will give it up and
         * spin until we've taken care of that timer below.
         */
        unlock_task_sighand(tsk, &flags);

        /*
         * Now that all the timers on our list have the firing flag,
         * no one will touch their list entries but us.  We'll take
         * each timer's lock before clearing its firing flag, so no
         * timer call will interfere.
         */
        list_for_each_entry_safe(timer, next, &firing, it.cpu.elist) {
                int cpu_firing;

                /*
                 * spin_lock() is sufficient here even independent of the
                 * expiry context. If expiry happens in hard interrupt
                 * context it's obvious. For task work context it's safe
                 * because all other operations on timer::it_lock happen in
                 * task context (syscall or exit).
                 */
                spin_lock(&timer->it_lock);
                list_del_init(&timer->it.cpu.elist);
                cpu_firing = timer->it.cpu.firing;
                timer->it.cpu.firing = 0;
                /*
                 * The firing flag is -1 if we collided with a reset
                 * of the timer, which already reported this
                 * almost-firing as an overrun.  So don't generate an event.
                 */
                if (likely(cpu_firing >= 0))
                        cpu_timer_fire(timer);
                /* See posix_cpu_timer_wait_running() */
                rcu_assign_pointer(timer->it.cpu.handling, NULL);
                spin_unlock(&timer->it_lock);
        }
}

/*
 * This is called from the timer interrupt handler.  The irq handler has
 * already updated our counts.  We need to check if any timers fire now.
 * Interrupts are disabled.
 */
void run_posix_cpu_timers(void)
{
        struct task_struct *tsk = current;

        lockdep_assert_irqs_disabled();

        /*
         * If the actual expiry is deferred to task work context and the
         * work is already scheduled there is no point to do anything here.
         */
        if (posix_cpu_timers_work_scheduled(tsk))
                return;

        /*
         * The fast path checks that there are no expired thread or thread
         * group timers.  If that's so, just return.
         */
        if (!fastpath_timer_check(tsk))
                return;

        __run_posix_cpu_timers(tsk);
}

/*
 * Set one of the process-wide special case CPU timers or RLIMIT_CPU.
 * The tsk->sighand->siglock must be held by the caller.
 */
void set_process_cpu_timer(struct task_struct *tsk, unsigned int clkid,
                           u64 *newval, u64 *oldval)
{
        u64 now, *nextevt;

        if (WARN_ON_ONCE(clkid >= CPUCLOCK_SCHED))
                return;

        nextevt = &tsk->signal->posix_cputimers.bases[clkid].nextevt;
        now = cpu_clock_sample_group(clkid, tsk, true);

        if (oldval) {
                /*
                 * We are setting itimer. The *oldval is absolute and we update
                 * it to be relative, *newval argument is relative and we update
                 * it to be absolute.
                 */
                if (*oldval) {
                        if (*oldval <= now) {
                                /* Just about to fire. */
                                *oldval = TICK_NSEC;
                        } else {
                                *oldval -= now;
                        }
                }

                if (*newval)
                        *newval += now;
        }

        /*
         * Update expiration cache if this is the earliest timer. CPUCLOCK_PROF
         * expiry cache is also used by RLIMIT_CPU!.
         */
        if (*newval < *nextevt)
                *nextevt = *newval;

        tick_dep_set_signal(tsk, TICK_DEP_BIT_POSIX_TIMER);
}

static int do_cpu_nanosleep(const clockid_t which_clock, int flags,
                            const struct timespec64 *rqtp)
{
        struct itimerspec64 it;
        struct k_itimer timer;
        u64 expires;
        int error;

        /*
         * Set up a temporary timer and then wait for it to go off.
         */
        memset(&timer, 0, sizeof timer);
        spin_lock_init(&timer.it_lock);
        timer.it_clock = which_clock;
        timer.it_overrun = -1;
        error = posix_cpu_timer_create(&timer);
        timer.it_process = current;

        if (!error) {
                static struct itimerspec64 zero_it;
                struct restart_block *restart;

                memset(&it, 0, sizeof(it));
                it.it_value = *rqtp;

                spin_lock_irq(&timer.it_lock);
                error = posix_cpu_timer_set(&timer, flags, &it, NULL);
                if (error) {
                        spin_unlock_irq(&timer.it_lock);
                        return error;
                }

                while (!signal_pending(current)) {
                        if (!cpu_timer_getexpires(&timer.it.cpu)) {
                                /*
                                 * Our timer fired and was reset, below
                                 * deletion can not fail.
                                 */
                                posix_cpu_timer_del(&timer);
                                spin_unlock_irq(&timer.it_lock);
                                return 0;
                        }

                        /*
                         * Block until cpu_timer_fire (or a signal) wakes us.
                         */
                        __set_current_state(TASK_INTERRUPTIBLE);
                        spin_unlock_irq(&timer.it_lock);
                        schedule();
                        spin_lock_irq(&timer.it_lock);
                }

                /*
                 * We were interrupted by a signal.
                 */
                expires = cpu_timer_getexpires(&timer.it.cpu);
                error = posix_cpu_timer_set(&timer, 0, &zero_it, &it);
                if (!error) {
                        /* Timer is now unarmed, deletion can not fail. */
                        posix_cpu_timer_del(&timer);
                } else {
                        while (error == TIMER_RETRY) {
                                posix_cpu_timer_wait_running_nsleep(&timer);
                                error = posix_cpu_timer_del(&timer);
                        }
                }

                spin_unlock_irq(&timer.it_lock);

                if ((it.it_value.tv_sec | it.it_value.tv_nsec) == 0) {
                        /*
                         * It actually did fire already.
                         */
                        return 0;
                }

                error = -ERESTART_RESTARTBLOCK;
                /*
                 * Report back to the user the time still remaining.
                 */
                restart = &current->restart_block;
                restart->nanosleep.expires = expires;
                if (restart->nanosleep.type != TT_NONE)
                        error = nanosleep_copyout(restart, &it.it_value);
        }

        return error;
}

static long posix_cpu_nsleep_restart(struct restart_block *restart_block);

static int posix_cpu_nsleep(const clockid_t which_clock, int flags,
                            const struct timespec64 *rqtp)
{
        struct restart_block *restart_block = &current->restart_block;
        int error;

        /*
         * Diagnose required errors first.
         */
        if (CPUCLOCK_PERTHREAD(which_clock) &&
            (CPUCLOCK_PID(which_clock) == 0 ||
             CPUCLOCK_PID(which_clock) == task_pid_vnr(current)))
                return -EINVAL;

        error = do_cpu_nanosleep(which_clock, flags, rqtp);

        if (error == -ERESTART_RESTARTBLOCK) {

                if (flags & TIMER_ABSTIME)
                        return -ERESTARTNOHAND;

                restart_block->nanosleep.clockid = which_clock;
                set_restart_fn(restart_block, posix_cpu_nsleep_restart);
        }
        return error;
}

static long posix_cpu_nsleep_restart(struct restart_block *restart_block)
{
        clockid_t which_clock = restart_block->nanosleep.clockid;
        struct timespec64 t;

        t = ns_to_timespec64(restart_block->nanosleep.expires);

        return do_cpu_nanosleep(which_clock, TIMER_ABSTIME, &t);
}

#define PROCESS_CLOCK   make_process_cpuclock(0, CPUCLOCK_SCHED)
#define THREAD_CLOCK    make_thread_cpuclock(0, CPUCLOCK_SCHED)

static int process_cpu_clock_getres(const clockid_t which_clock,
                                    struct timespec64 *tp)
{
        return posix_cpu_clock_getres(PROCESS_CLOCK, tp);
}
static int process_cpu_clock_get(const clockid_t which_clock,
                                 struct timespec64 *tp)
{
        return posix_cpu_clock_get(PROCESS_CLOCK, tp);
}
static int process_cpu_timer_create(struct k_itimer *timer)
{
        timer->it_clock = PROCESS_CLOCK;
        return posix_cpu_timer_create(timer);
}
static int process_cpu_nsleep(const clockid_t which_clock, int flags,
                              const struct timespec64 *rqtp)
{
        return posix_cpu_nsleep(PROCESS_CLOCK, flags, rqtp);
}
static int thread_cpu_clock_getres(const clockid_t which_clock,
                                   struct timespec64 *tp)
{
        return posix_cpu_clock_getres(THREAD_CLOCK, tp);
}
static int thread_cpu_clock_get(const clockid_t which_clock,
                                struct timespec64 *tp)
{
        return posix_cpu_clock_get(THREAD_CLOCK, tp);
}
static int thread_cpu_timer_create(struct k_itimer *timer)
{
        timer->it_clock = THREAD_CLOCK;
        return posix_cpu_timer_create(timer);
}

const struct k_clock clock_posix_cpu = {
        .clock_getres           = posix_cpu_clock_getres,
        .clock_set              = posix_cpu_clock_set,
        .clock_get_timespec     = posix_cpu_clock_get,
        .timer_create           = posix_cpu_timer_create,
        .nsleep                 = posix_cpu_nsleep,
        .timer_set              = posix_cpu_timer_set,
        .timer_del              = posix_cpu_timer_del,
        .timer_get              = posix_cpu_timer_get,
        .timer_rearm            = posix_cpu_timer_rearm,
        .timer_wait_running     = posix_cpu_timer_wait_running,
};

const struct k_clock clock_process = {
        .clock_getres           = process_cpu_clock_getres,
        .clock_get_timespec     = process_cpu_clock_get,
        .timer_create           = process_cpu_timer_create,
        .nsleep                 = process_cpu_nsleep,
};

const struct k_clock clock_thread = {
        .clock_getres           = thread_cpu_clock_getres,
        .clock_get_timespec     = thread_cpu_clock_get,
        .timer_create           = thread_cpu_timer_create,
};