kernel/sched/stop_task.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * stop-task scheduling class.
   4  *
   5  * The stop task is the highest priority task in the system, it preempts
   6  * everything and will be preempted by nothing.
   7  *
   8  * See kernel/stop_machine.c
   9  */
  10 #include "sched.h"
  11
  12 #ifdef CONFIG_SMP
  13 static int
  14 select_task_rq_stop(struct task_struct *p, int cpu, int flags)
  15 {
  16         return task_cpu(p); /* stop tasks as never migrate */
  17 }
  18
  19 static int
  20 balance_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
  21 {
  22         return sched_stop_runnable(rq);
  23 }
  24 #endif /* CONFIG_SMP */
  25
  26 static void
  27 check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
  28 {
  29         /* we're never preempted */
  30 }
  31
  32 static void set_next_task_stop(struct rq *rq, struct task_struct *stop, bool first)
  33 {
  34         stop->se.exec_start = rq_clock_task(rq);
  35 }
  36
  37 static struct task_struct *pick_task_stop(struct rq *rq)
  38 {
  39         if (!sched_stop_runnable(rq))
  40                 return NULL;
  41
  42         return rq->stop;
  43 }
  44
  45 static struct task_struct *pick_next_task_stop(struct rq *rq)
  46 {
  47         struct task_struct *p = pick_task_stop(rq);
  48
  49         if (p)
  50                 set_next_task_stop(rq, p, true);
  51
  52         return p;
  53 }
  54
  55 static void
  56 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  57 {
  58         add_nr_running(rq, 1);
  59 }
  60
  61 static void
  62 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  63 {
  64         sub_nr_running(rq, 1);
  65 }
  66
  67 static void yield_task_stop(struct rq *rq)
  68 {
  69         BUG(); /* the stop task should never yield, its pointless. */
  70 }
  71
  72 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
  73 {
  74         struct task_struct *curr = rq->curr;
  75         u64 delta_exec;
  76
  77         delta_exec = rq_clock_task(rq) - curr->se.exec_start;
  78         if (unlikely((s64)delta_exec < 0))
  79                 delta_exec = 0;
  80
  81         schedstat_set(curr->se.statistics.exec_max,
  82                         max(curr->se.statistics.exec_max, delta_exec));
  83
  84         curr->se.sum_exec_runtime += delta_exec;
  85         account_group_exec_runtime(curr, delta_exec);
  86
  87         curr->se.exec_start = rq_clock_task(rq);
  88         cgroup_account_cputime(curr, delta_exec);
  89 }
  90
  91 /*
  92  * scheduler tick hitting a task of our scheduling class.
  93  *
  94  * NOTE: This function can be called remotely by the tick offload that
  95  * goes along full dynticks. Therefore no local assumption can be made
  96  * and everything must be accessed through the @rq and @curr passed in
  97  * parameters.
  98  */
  99 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
 100 {
 101 }
 102
 103 static void switched_to_stop(struct rq *rq, struct task_struct *p)
 104 {
 105         BUG(); /* its impossible to change to this class */
 106 }
 107
 108 static void
 109 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
 110 {
 111         BUG(); /* how!?, what priority? */
 112 }
 113
 114 static void update_curr_stop(struct rq *rq)
 115 {
 116 }
 117
 118 /*
 119  * Simple, special scheduling class for the per-CPU stop tasks:
 120  */
 121 DEFINE_SCHED_CLASS(stop) = {
 122
 123         .enqueue_task           = enqueue_task_stop,
 124         .dequeue_task           = dequeue_task_stop,
 125         .yield_task             = yield_task_stop,
 126
 127         .check_preempt_curr     = check_preempt_curr_stop,
 128
 129         .pick_next_task         = pick_next_task_stop,
 130         .put_prev_task          = put_prev_task_stop,
 131         .set_next_task          = set_next_task_stop,
 132
 133 #ifdef CONFIG_SMP
 134         .balance                = balance_stop,
 135         .pick_task              = pick_task_stop,
 136         .select_task_rq         = select_task_rq_stop,
 137         .set_cpus_allowed       = set_cpus_allowed_common,
 138 #endif
 139
 140         .task_tick              = task_tick_stop,
 141
 142         .prio_changed           = prio_changed_stop,
 143         .switched_to            = switched_to_stop,
 144         .update_curr            = update_curr_stop,
 145 };