kernel/kernel/sched/wait-simple.c

   1 /*
   2  * Simple waitqueues without fancy flags and callbacks
   3  *
   4  * (C) 2011 Thomas Gleixner <tglx@linutronix.de>
   5  *
   6  * Based on kernel/wait.c
   7  *
   8  * For licencing details see kernel-base/COPYING
   9  */
  10 #include <linux/init.h>
  11 #include <linux/export.h>
  12 #include <linux/sched.h>
  13 #include <linux/wait-simple.h>
  14
  15 /* Adds w to head->list. Must be called with head->lock locked. */
  16 static inline void __swait_enqueue(struct swait_head *head, struct swaiter *w)
  17 {
  18         list_add(&w->node, &head->list);
  19         /* We can't let the condition leak before the setting of head */
  20         smp_mb();
  21 }
  22
  23 /* Removes w from head->list. Must be called with head->lock locked. */
  24 static inline void __swait_dequeue(struct swaiter *w)
  25 {
  26         list_del_init(&w->node);
  27 }
  28
  29 void __init_swait_head(struct swait_head *head, struct lock_class_key *key)
  30 {
  31         raw_spin_lock_init(&head->lock);
  32         lockdep_set_class(&head->lock, key);
  33         INIT_LIST_HEAD(&head->list);
  34 }
  35 EXPORT_SYMBOL(__init_swait_head);
  36
  37 void swait_prepare_locked(struct swait_head *head, struct swaiter *w)
  38 {
  39         w->task = current;
  40         if (list_empty(&w->node))
  41                 __swait_enqueue(head, w);
  42 }
  43
  44 void swait_prepare(struct swait_head *head, struct swaiter *w, int state)
  45 {
  46         unsigned long flags;
  47
  48         raw_spin_lock_irqsave(&head->lock, flags);
  49         swait_prepare_locked(head, w);
  50         __set_current_state(state);
  51         raw_spin_unlock_irqrestore(&head->lock, flags);
  52 }
  53 EXPORT_SYMBOL(swait_prepare);
  54
  55 void swait_finish_locked(struct swait_head *head, struct swaiter *w)
  56 {
  57         __set_current_state(TASK_RUNNING);
  58         if (w->task)
  59                 __swait_dequeue(w);
  60 }
  61
  62 void swait_finish(struct swait_head *head, struct swaiter *w)
  63 {
  64         unsigned long flags;
  65
  66         __set_current_state(TASK_RUNNING);
  67         if (w->task) {
  68                 raw_spin_lock_irqsave(&head->lock, flags);
  69                 __swait_dequeue(w);
  70                 raw_spin_unlock_irqrestore(&head->lock, flags);
  71         }
  72 }
  73 EXPORT_SYMBOL(swait_finish);
  74
  75 unsigned int
  76 __swait_wake_locked(struct swait_head *head, unsigned int state, unsigned int num)
  77 {
  78         struct swaiter *curr, *next;
  79         int woken = 0;
  80
  81         list_for_each_entry_safe(curr, next, &head->list, node) {
  82                 if (wake_up_state(curr->task, state)) {
  83                         __swait_dequeue(curr);
  84                         /*
  85                          * The waiting task can free the waiter as
  86                          * soon as curr->task = NULL is written,
  87                          * without taking any locks. A memory barrier
  88                          * is required here to prevent the following
  89                          * store to curr->task from getting ahead of
  90                          * the dequeue operation.
  91                          */
  92                         smp_wmb();
  93                         curr->task = NULL;
  94                         if (++woken == num)
  95                                 break;
  96                 }
  97         }
  98         return woken;
  99 }
 100
 101 unsigned int
 102 __swait_wake(struct swait_head *head, unsigned int state, unsigned int num)
 103 {
 104         unsigned long flags;
 105         int woken;
 106
 107         if (!swaitqueue_active(head))
 108                 return 0;
 109
 110         raw_spin_lock_irqsave(&head->lock, flags);
 111         woken = __swait_wake_locked(head, state, num);
 112         raw_spin_unlock_irqrestore(&head->lock, flags);
 113         return woken;
 114 }
 115 EXPORT_SYMBOL(__swait_wake);