2 * Generic waiting primitives.
4 * (C) 2004 Nadia Yvette Chambers, Oracle
6 #include <linux/init.h>
7 #include <linux/export.h>
8 #include <linux/sched/signal.h>
9 #include <linux/sched/debug.h>
11 #include <linux/wait.h>
12 #include <linux/hash.h>
13 #include <linux/kthread.h>
15 void __init_waitqueue_head(struct wait_queue_head *wq_head, const char *name, struct lock_class_key *key)
17 spin_lock_init(&wq_head->lock);
18 lockdep_set_class_and_name(&wq_head->lock, key, name);
19 INIT_LIST_HEAD(&wq_head->head);
22 EXPORT_SYMBOL(__init_waitqueue_head);
24 void add_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
28 wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
29 spin_lock_irqsave(&wq_head->lock, flags);
30 __add_wait_queue_entry_tail(wq_head, wq_entry);
31 spin_unlock_irqrestore(&wq_head->lock, flags);
33 EXPORT_SYMBOL(add_wait_queue);
35 void add_wait_queue_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
39 wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
40 spin_lock_irqsave(&wq_head->lock, flags);
41 __add_wait_queue_entry_tail(wq_head, wq_entry);
42 spin_unlock_irqrestore(&wq_head->lock, flags);
44 EXPORT_SYMBOL(add_wait_queue_exclusive);
46 void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
50 spin_lock_irqsave(&wq_head->lock, flags);
51 __remove_wait_queue(wq_head, wq_entry);
52 spin_unlock_irqrestore(&wq_head->lock, flags);
54 EXPORT_SYMBOL(remove_wait_queue);
58 * The core wakeup function. Non-exclusive wakeups (nr_exclusive == 0) just
59 * wake everything up. If it's an exclusive wakeup (nr_exclusive == small +ve
60 * number) then we wake all the non-exclusive tasks and one exclusive task.
62 * There are circumstances in which we can try to wake a task which has already
63 * started to run but is not in state TASK_RUNNING. try_to_wake_up() returns
64 * zero in this (rare) case, and we handle it by continuing to scan the queue.
66 static void __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode,
67 int nr_exclusive, int wake_flags, void *key)
69 wait_queue_entry_t *curr, *next;
71 list_for_each_entry_safe(curr, next, &wq_head->head, entry) {
72 unsigned flags = curr->flags;
73 int ret = curr->func(curr, mode, wake_flags, key);
76 if (ret && (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
82 * __wake_up - wake up threads blocked on a waitqueue.
83 * @wq_head: the waitqueue
84 * @mode: which threads
85 * @nr_exclusive: how many wake-one or wake-many threads to wake up
86 * @key: is directly passed to the wakeup function
88 * It may be assumed that this function implies a write memory barrier before
89 * changing the task state if and only if any tasks are woken up.
91 void __wake_up(struct wait_queue_head *wq_head, unsigned int mode,
92 int nr_exclusive, void *key)
96 spin_lock_irqsave(&wq_head->lock, flags);
97 __wake_up_common(wq_head, mode, nr_exclusive, 0, key);
98 spin_unlock_irqrestore(&wq_head->lock, flags);
100 EXPORT_SYMBOL(__wake_up);
103 * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
105 void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr)
107 __wake_up_common(wq_head, mode, nr, 0, NULL);
109 EXPORT_SYMBOL_GPL(__wake_up_locked);
111 void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key)
113 __wake_up_common(wq_head, mode, 1, 0, key);
115 EXPORT_SYMBOL_GPL(__wake_up_locked_key);
118 * __wake_up_sync_key - wake up threads blocked on a waitqueue.
119 * @wq_head: the waitqueue
120 * @mode: which threads
121 * @nr_exclusive: how many wake-one or wake-many threads to wake up
122 * @key: opaque value to be passed to wakeup targets
124 * The sync wakeup differs that the waker knows that it will schedule
125 * away soon, so while the target thread will be woken up, it will not
126 * be migrated to another CPU - ie. the two threads are 'synchronized'
127 * with each other. This can prevent needless bouncing between CPUs.
129 * On UP it can prevent extra preemption.
131 * It may be assumed that this function implies a write memory barrier before
132 * changing the task state if and only if any tasks are woken up.
134 void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode,
135 int nr_exclusive, void *key)
138 int wake_flags = 1; /* XXX WF_SYNC */
140 if (unlikely(!wq_head))
143 if (unlikely(nr_exclusive != 1))
146 spin_lock_irqsave(&wq_head->lock, flags);
147 __wake_up_common(wq_head, mode, nr_exclusive, wake_flags, key);
148 spin_unlock_irqrestore(&wq_head->lock, flags);
150 EXPORT_SYMBOL_GPL(__wake_up_sync_key);
153 * __wake_up_sync - see __wake_up_sync_key()
155 void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode, int nr_exclusive)
157 __wake_up_sync_key(wq_head, mode, nr_exclusive, NULL);
159 EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */
162 * Note: we use "set_current_state()" _after_ the wait-queue add,
163 * because we need a memory barrier there on SMP, so that any
164 * wake-function that tests for the wait-queue being active
165 * will be guaranteed to see waitqueue addition _or_ subsequent
166 * tests in this thread will see the wakeup having taken place.
168 * The spin_unlock() itself is semi-permeable and only protects
169 * one way (it only protects stuff inside the critical region and
170 * stops them from bleeding out - it would still allow subsequent
171 * loads to move into the critical region).
174 prepare_to_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
178 wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
179 spin_lock_irqsave(&wq_head->lock, flags);
180 if (list_empty(&wq_entry->entry))
181 __add_wait_queue(wq_head, wq_entry);
182 set_current_state(state);
183 spin_unlock_irqrestore(&wq_head->lock, flags);
185 EXPORT_SYMBOL(prepare_to_wait);
188 prepare_to_wait_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
192 wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
193 spin_lock_irqsave(&wq_head->lock, flags);
194 if (list_empty(&wq_entry->entry))
195 __add_wait_queue_entry_tail(wq_head, wq_entry);
196 set_current_state(state);
197 spin_unlock_irqrestore(&wq_head->lock, flags);
199 EXPORT_SYMBOL(prepare_to_wait_exclusive);
201 void init_wait_entry(struct wait_queue_entry *wq_entry, int flags)
203 wq_entry->flags = flags;
204 wq_entry->private = current;
205 wq_entry->func = autoremove_wake_function;
206 INIT_LIST_HEAD(&wq_entry->entry);
208 EXPORT_SYMBOL(init_wait_entry);
210 long prepare_to_wait_event(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
215 spin_lock_irqsave(&wq_head->lock, flags);
216 if (unlikely(signal_pending_state(state, current))) {
218 * Exclusive waiter must not fail if it was selected by wakeup,
219 * it should "consume" the condition we were waiting for.
221 * The caller will recheck the condition and return success if
222 * we were already woken up, we can not miss the event because
223 * wakeup locks/unlocks the same wq_head->lock.
225 * But we need to ensure that set-condition + wakeup after that
226 * can't see us, it should wake up another exclusive waiter if
229 list_del_init(&wq_entry->entry);
232 if (list_empty(&wq_entry->entry)) {
233 if (wq_entry->flags & WQ_FLAG_EXCLUSIVE)
234 __add_wait_queue_entry_tail(wq_head, wq_entry);
236 __add_wait_queue(wq_head, wq_entry);
238 set_current_state(state);
240 spin_unlock_irqrestore(&wq_head->lock, flags);
244 EXPORT_SYMBOL(prepare_to_wait_event);
247 * Note! These two wait functions are entered with the
248 * wait-queue lock held (and interrupts off in the _irq
249 * case), so there is no race with testing the wakeup
250 * condition in the caller before they add the wait
251 * entry to the wake queue.
253 int do_wait_intr(wait_queue_head_t *wq, wait_queue_entry_t *wait)
255 if (likely(list_empty(&wait->entry)))
256 __add_wait_queue_entry_tail(wq, wait);
258 set_current_state(TASK_INTERRUPTIBLE);
259 if (signal_pending(current))
262 spin_unlock(&wq->lock);
264 spin_lock(&wq->lock);
267 EXPORT_SYMBOL(do_wait_intr);
269 int do_wait_intr_irq(wait_queue_head_t *wq, wait_queue_entry_t *wait)
271 if (likely(list_empty(&wait->entry)))
272 __add_wait_queue_entry_tail(wq, wait);
274 set_current_state(TASK_INTERRUPTIBLE);
275 if (signal_pending(current))
278 spin_unlock_irq(&wq->lock);
280 spin_lock_irq(&wq->lock);
283 EXPORT_SYMBOL(do_wait_intr_irq);
286 * finish_wait - clean up after waiting in a queue
287 * @wq_head: waitqueue waited on
288 * @wq_entry: wait descriptor
290 * Sets current thread back to running state and removes
291 * the wait descriptor from the given waitqueue if still
294 void finish_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
298 __set_current_state(TASK_RUNNING);
300 * We can check for list emptiness outside the lock
302 * - we use the "careful" check that verifies both
303 * the next and prev pointers, so that there cannot
304 * be any half-pending updates in progress on other
305 * CPU's that we haven't seen yet (and that might
306 * still change the stack area.
308 * - all other users take the lock (ie we can only
309 * have _one_ other CPU that looks at or modifies
312 if (!list_empty_careful(&wq_entry->entry)) {
313 spin_lock_irqsave(&wq_head->lock, flags);
314 list_del_init(&wq_entry->entry);
315 spin_unlock_irqrestore(&wq_head->lock, flags);
318 EXPORT_SYMBOL(finish_wait);
320 int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
322 int ret = default_wake_function(wq_entry, mode, sync, key);
325 list_del_init(&wq_entry->entry);
328 EXPORT_SYMBOL(autoremove_wake_function);
330 static inline bool is_kthread_should_stop(void)
332 return (current->flags & PF_KTHREAD) && kthread_should_stop();
336 * DEFINE_WAIT_FUNC(wait, woken_wake_func);
338 * add_wait_queue(&wq_head, &wait);
343 * p->state = mode; condition = true;
344 * smp_mb(); // A smp_wmb(); // C
345 * if (!wq_entry->flags & WQ_FLAG_WOKEN) wq_entry->flags |= WQ_FLAG_WOKEN;
346 * schedule() try_to_wake_up();
347 * p->state = TASK_RUNNING; ~~~~~~~~~~~~~~~~~~
348 * wq_entry->flags &= ~WQ_FLAG_WOKEN; condition = true;
349 * smp_mb() // B smp_wmb(); // C
350 * wq_entry->flags |= WQ_FLAG_WOKEN;
352 * remove_wait_queue(&wq_head, &wait);
355 long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout)
357 set_current_state(mode); /* A */
359 * The above implies an smp_mb(), which matches with the smp_wmb() from
360 * woken_wake_function() such that if we observe WQ_FLAG_WOKEN we must
361 * also observe all state before the wakeup.
363 if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
364 timeout = schedule_timeout(timeout);
365 __set_current_state(TASK_RUNNING);
368 * The below implies an smp_mb(), it too pairs with the smp_wmb() from
369 * woken_wake_function() such that we must either observe the wait
370 * condition being true _OR_ WQ_FLAG_WOKEN such that we will not miss
373 smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */
377 EXPORT_SYMBOL(wait_woken);
379 int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
382 * Although this function is called under waitqueue lock, LOCK
383 * doesn't imply write barrier and the users expects write
384 * barrier semantics on wakeup functions. The following
385 * smp_wmb() is equivalent to smp_wmb() in try_to_wake_up()
386 * and is paired with smp_store_mb() in wait_woken().
389 wq_entry->flags |= WQ_FLAG_WOKEN;
391 return default_wake_function(wq_entry, mode, sync, key);
393 EXPORT_SYMBOL(woken_wake_function);