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 sd_flag, 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 *
  38 pick_next_task_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
  39 {
  40         WARN_ON_ONCE(prev || rf);
  41
  42         if (!sched_stop_runnable(rq))
  43                 return NULL;
  44
  45         set_next_task_stop(rq, rq->stop, true);
  46         return rq->stop;
  47 }
  48
  49 static void
  50 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  51 {
  52         add_nr_running(rq, 1);
  53 }
  54
  55 static void
  56 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  57 {
  58         sub_nr_running(rq, 1);
  59 }
  60
  61 static void yield_task_stop(struct rq *rq)
  62 {
  63         BUG(); /* the stop task should never yield, its pointless. */
  64 }
  65
  66 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
  67 {
  68         struct task_struct *curr = rq->curr;
  69         u64 delta_exec;
  70
  71         delta_exec = rq_clock_task(rq) - curr->se.exec_start;
  72         if (unlikely((s64)delta_exec < 0))
  73                 delta_exec = 0;
  74
  75         schedstat_set(curr->se.statistics.exec_max,
  76                         max(curr->se.statistics.exec_max, delta_exec));
  77
  78         curr->se.sum_exec_runtime += delta_exec;
  79         account_group_exec_runtime(curr, delta_exec);
  80
  81         curr->se.exec_start = rq_clock_task(rq);
  82         cgroup_account_cputime(curr, delta_exec);
  83 }
  84
  85 /*
  86  * scheduler tick hitting a task of our scheduling class.
  87  *
  88  * NOTE: This function can be called remotely by the tick offload that
  89  * goes along full dynticks. Therefore no local assumption can be made
  90  * and everything must be accessed through the @rq and @curr passed in
  91  * parameters.
  92  */
  93 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
  94 {
  95 }
  96
  97 static void switched_to_stop(struct rq *rq, struct task_struct *p)
  98 {
  99         BUG(); /* its impossible to change to this class */
 100 }
 101
 102 static void
 103 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
 104 {
 105         BUG(); /* how!?, what priority? */
 106 }
 107
 108 static unsigned int
 109 get_rr_interval_stop(struct rq *rq, struct task_struct *task)
 110 {
 111         return 0;
 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 const struct sched_class stop_sched_class = {
 122         .next                   = &dl_sched_class,
 123
 124         .enqueue_task           = enqueue_task_stop,
 125         .dequeue_task           = dequeue_task_stop,
 126         .yield_task             = yield_task_stop,
 127
 128         .check_preempt_curr     = check_preempt_curr_stop,
 129
 130         .pick_next_task         = pick_next_task_stop,
 131         .put_prev_task          = put_prev_task_stop,
 132         .set_next_task          = set_next_task_stop,
 133
 134 #ifdef CONFIG_SMP
 135         .balance                = balance_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         .get_rr_interval        = get_rr_interval_stop,
 143
 144         .prio_changed           = prio_changed_stop,
 145         .switched_to            = switched_to_stop,
 146         .update_curr            = update_curr_stop,
 147 };