kernel/sched/swait.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * <linux/swait.h> (simple wait queues ) implementation:
   4  */
   5 #include "sched.h"
   6
   7 void __init_swait_queue_head(struct swait_queue_head *q, const char *name,
   8                              struct lock_class_key *key)
   9 {
  10         raw_spin_lock_init(&q->lock);
  11         lockdep_set_class_and_name(&q->lock, key, name);
  12         INIT_LIST_HEAD(&q->task_list);
  13 }
  14 EXPORT_SYMBOL(__init_swait_queue_head);
  15
  16 /*
  17  * The thing about the wake_up_state() return value; I think we can ignore it.
  18  *
  19  * If for some reason it would return 0, that means the previously waiting
  20  * task is already running, so it will observe condition true (or has already).
  21  */
  22 void swake_up_locked(struct swait_queue_head *q)
  23 {
  24         struct swait_queue *curr;
  25
  26         if (list_empty(&q->task_list))
  27                 return;
  28
  29         curr = list_first_entry(&q->task_list, typeof(*curr), task_list);
  30         wake_up_process(curr->task);
  31         list_del_init(&curr->task_list);
  32 }
  33 EXPORT_SYMBOL(swake_up_locked);
  34
  35 /*
  36  * Wake up all waiters. This is an interface which is solely exposed for
  37  * completions and not for general usage.
  38  *
  39  * It is intentionally different from swake_up_all() to allow usage from
  40  * hard interrupt context and interrupt disabled regions.
  41  */
  42 void swake_up_all_locked(struct swait_queue_head *q)
  43 {
  44         while (!list_empty(&q->task_list))
  45                 swake_up_locked(q);
  46 }
  47
  48 void swake_up_one(struct swait_queue_head *q)
  49 {
  50         unsigned long flags;
  51
  52         raw_spin_lock_irqsave(&q->lock, flags);
  53         swake_up_locked(q);
  54         raw_spin_unlock_irqrestore(&q->lock, flags);
  55 }
  56 EXPORT_SYMBOL(swake_up_one);
  57
  58 /*
  59  * Does not allow usage from IRQ disabled, since we must be able to
  60  * release IRQs to guarantee bounded hold time.
  61  */
  62 void swake_up_all(struct swait_queue_head *q)
  63 {
  64         struct swait_queue *curr;
  65         LIST_HEAD(tmp);
  66
  67         WARN_ON(irqs_disabled());
  68         raw_spin_lock_irq(&q->lock);
  69         list_splice_init(&q->task_list, &tmp);
  70         while (!list_empty(&tmp)) {
  71                 curr = list_first_entry(&tmp, typeof(*curr), task_list);
  72
  73                 wake_up_state(curr->task, TASK_NORMAL);
  74                 list_del_init(&curr->task_list);
  75
  76                 if (list_empty(&tmp))
  77                         break;
  78
  79                 raw_spin_unlock_irq(&q->lock);
  80                 raw_spin_lock_irq(&q->lock);
  81         }
  82         raw_spin_unlock_irq(&q->lock);
  83 }
  84 EXPORT_SYMBOL(swake_up_all);
  85
  86 void __prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait)
  87 {
  88         wait->task = current;
  89         if (list_empty(&wait->task_list))
  90                 list_add_tail(&wait->task_list, &q->task_list);
  91 }
  92
  93 void prepare_to_swait_exclusive(struct swait_queue_head *q, struct swait_queue *wait, int state)
  94 {
  95         unsigned long flags;
  96
  97         raw_spin_lock_irqsave(&q->lock, flags);
  98         __prepare_to_swait(q, wait);
  99         set_current_state(state);
 100         raw_spin_unlock_irqrestore(&q->lock, flags);
 101 }
 102 EXPORT_SYMBOL(prepare_to_swait_exclusive);
 103
 104 long prepare_to_swait_event(struct swait_queue_head *q, struct swait_queue *wait, int state)
 105 {
 106         unsigned long flags;
 107         long ret = 0;
 108
 109         raw_spin_lock_irqsave(&q->lock, flags);
 110         if (signal_pending_state(state, current)) {
 111                 /*
 112                  * See prepare_to_wait_event(). TL;DR, subsequent swake_up_one()
 113                  * must not see us.
 114                  */
 115                 list_del_init(&wait->task_list);
 116                 ret = -ERESTARTSYS;
 117         } else {
 118                 __prepare_to_swait(q, wait);
 119                 set_current_state(state);
 120         }
 121         raw_spin_unlock_irqrestore(&q->lock, flags);
 122
 123         return ret;
 124 }
 125 EXPORT_SYMBOL(prepare_to_swait_event);
 126
 127 void __finish_swait(struct swait_queue_head *q, struct swait_queue *wait)
 128 {
 129         __set_current_state(TASK_RUNNING);
 130         if (!list_empty(&wait->task_list))
 131                 list_del_init(&wait->task_list);
 132 }
 133
 134 void finish_swait(struct swait_queue_head *q, struct swait_queue *wait)
 135 {
 136         unsigned long flags;
 137
 138         __set_current_state(TASK_RUNNING);
 139
 140         if (!list_empty_careful(&wait->task_list)) {
 141                 raw_spin_lock_irqsave(&q->lock, flags);
 142                 list_del_init(&wait->task_list);
 143                 raw_spin_unlock_irqrestore(&q->lock, flags);
 144         }
 145 }
 146 EXPORT_SYMBOL(finish_swait);