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_next_task_stop(struct rq *rq)
  38 {
  39         if (!sched_stop_runnable(rq))
  40                 return NULL;
  41
  42         set_next_task_stop(rq, rq->stop, true);
  43         return rq->stop;
  44 }
  45
  46 static void
  47 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  48 {
  49         add_nr_running(rq, 1);
  50 }
  51
  52 static void
  53 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  54 {
  55         sub_nr_running(rq, 1);
  56 }
  57
  58 static void yield_task_stop(struct rq *rq)
  59 {
  60         BUG(); /* the stop task should never yield, its pointless. */
  61 }
  62
  63 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
  64 {
  65         struct task_struct *curr = rq->curr;
  66         u64 delta_exec;
  67
  68         delta_exec = rq_clock_task(rq) - curr->se.exec_start;
  69         if (unlikely((s64)delta_exec < 0))
  70                 delta_exec = 0;
  71
  72         schedstat_set(curr->se.statistics.exec_max,
  73                         max(curr->se.statistics.exec_max, delta_exec));
  74
  75         curr->se.sum_exec_runtime += delta_exec;
  76         account_group_exec_runtime(curr, delta_exec);
  77
  78         curr->se.exec_start = rq_clock_task(rq);
  79         cgroup_account_cputime(curr, delta_exec);
  80 }
  81
  82 /*
  83  * scheduler tick hitting a task of our scheduling class.
  84  *
  85  * NOTE: This function can be called remotely by the tick offload that
  86  * goes along full dynticks. Therefore no local assumption can be made
  87  * and everything must be accessed through the @rq and @curr passed in
  88  * parameters.
  89  */
  90 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
  91 {
  92 }
  93
  94 static void switched_to_stop(struct rq *rq, struct task_struct *p)
  95 {
  96         BUG(); /* its impossible to change to this class */
  97 }
  98
  99 static void
 100 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
 101 {
 102         BUG(); /* how!?, what priority? */
 103 }
 104
 105 static void update_curr_stop(struct rq *rq)
 106 {
 107 }
 108
 109 /*
 110  * Simple, special scheduling class for the per-CPU stop tasks:
 111  */
 112 DEFINE_SCHED_CLASS(stop) = {
 113
 114         .enqueue_task           = enqueue_task_stop,
 115         .dequeue_task           = dequeue_task_stop,
 116         .yield_task             = yield_task_stop,
 117
 118         .check_preempt_curr     = check_preempt_curr_stop,
 119
 120         .pick_next_task         = pick_next_task_stop,
 121         .put_prev_task          = put_prev_task_stop,
 122         .set_next_task          = set_next_task_stop,
 123
 124 #ifdef CONFIG_SMP
 125         .balance                = balance_stop,
 126         .select_task_rq         = select_task_rq_stop,
 127         .set_cpus_allowed       = set_cpus_allowed_common,
 128 #endif
 129
 130         .task_tick              = task_tick_stop,
 131
 132         .prio_changed           = prio_changed_stop,
 133         .switched_to            = switched_to_stop,
 134         .update_curr            = update_curr_stop,
 135 };