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
  11 #ifdef CONFIG_SMP
  12 static int
  13 select_task_rq_stop(struct task_struct *p, int cpu, int flags)
  14 {
  15         return task_cpu(p); /* stop tasks as never migrate */
  16 }
  17
  18 static int
  19 balance_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
  20 {
  21         return sched_stop_runnable(rq);
  22 }
  23 #endif /* CONFIG_SMP */
  24
  25 static void
  26 wakeup_preempt_stop(struct rq *rq, struct task_struct *p, int flags)
  27 {
  28         /* we're never preempted */
  29 }
  30
  31 static void set_next_task_stop(struct rq *rq, struct task_struct *stop, bool first)
  32 {
  33         stop->se.exec_start = rq_clock_task(rq);
  34 }
  35
  36 static struct task_struct *pick_task_stop(struct rq *rq)
  37 {
  38         if (!sched_stop_runnable(rq))
  39                 return NULL;
  40
  41         return rq->stop;
  42 }
  43
  44 static void
  45 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  46 {
  47         add_nr_running(rq, 1);
  48 }
  49
  50 static bool
  51 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
  52 {
  53         sub_nr_running(rq, 1);
  54         return true;
  55 }
  56
  57 static void yield_task_stop(struct rq *rq)
  58 {
  59         BUG(); /* the stop task should never yield, its pointless. */
  60 }
  61
  62 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev, struct task_struct *next)
  63 {
  64         update_curr_common(rq);
  65 }
  66
  67 /*
  68  * scheduler tick hitting a task of our scheduling class.
  69  *
  70  * NOTE: This function can be called remotely by the tick offload that
  71  * goes along full dynticks. Therefore no local assumption can be made
  72  * and everything must be accessed through the @rq and @curr passed in
  73  * parameters.
  74  */
  75 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
  76 {
  77 }
  78
  79 static void switched_to_stop(struct rq *rq, struct task_struct *p)
  80 {
  81         BUG(); /* its impossible to change to this class */
  82 }
  83
  84 static void
  85 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
  86 {
  87         BUG(); /* how!?, what priority? */
  88 }
  89
  90 static void update_curr_stop(struct rq *rq)
  91 {
  92 }
  93
  94 /*
  95  * Simple, special scheduling class for the per-CPU stop tasks:
  96  */
  97 DEFINE_SCHED_CLASS(stop) = {
  98
  99         .enqueue_task           = enqueue_task_stop,
 100         .dequeue_task           = dequeue_task_stop,
 101         .yield_task             = yield_task_stop,
 102
 103         .wakeup_preempt         = wakeup_preempt_stop,
 104
 105         .pick_task              = pick_task_stop,
 106         .put_prev_task          = put_prev_task_stop,
 107         .set_next_task          = set_next_task_stop,
 108
 109 #ifdef CONFIG_SMP
 110         .balance                = balance_stop,
 111         .select_task_rq         = select_task_rq_stop,
 112         .set_cpus_allowed       = set_cpus_allowed_common,
 113 #endif
 114
 115         .task_tick              = task_tick_stop,
 116
 117         .prio_changed           = prio_changed_stop,
 118         .switched_to            = switched_to_stop,
 119         .update_curr            = update_curr_stop,
 120 };