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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Generic waiting primitives.
4 *
5 * (C) 2004 Nadia Yvette Chambers, Oracle
6 */
7#include "sched.h"
8
9void __init_waitqueue_head(struct wait_queue_head *wq_head, const char *name, struct lock_class_key *key)
10{
11 spin_lock_init(&wq_head->lock);
12 lockdep_set_class_and_name(&wq_head->lock, key, name);
13 INIT_LIST_HEAD(&wq_head->head);
14}
15
16EXPORT_SYMBOL(__init_waitqueue_head);
17
18void add_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
19{
20 unsigned long flags;
21
22 wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
23 spin_lock_irqsave(&wq_head->lock, flags);
24 __add_wait_queue(wq_head, wq_entry);
25 spin_unlock_irqrestore(&wq_head->lock, flags);
26}
27EXPORT_SYMBOL(add_wait_queue);
28
29void add_wait_queue_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
30{
31 unsigned long flags;
32
33 wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
34 spin_lock_irqsave(&wq_head->lock, flags);
35 __add_wait_queue_entry_tail(wq_head, wq_entry);
36 spin_unlock_irqrestore(&wq_head->lock, flags);
37}
38EXPORT_SYMBOL(add_wait_queue_exclusive);
39
40void add_wait_queue_priority(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
41{
42 unsigned long flags;
43
44 wq_entry->flags |= WQ_FLAG_EXCLUSIVE | WQ_FLAG_PRIORITY;
45 spin_lock_irqsave(&wq_head->lock, flags);
46 __add_wait_queue(wq_head, wq_entry);
47 spin_unlock_irqrestore(&wq_head->lock, flags);
48}
49EXPORT_SYMBOL_GPL(add_wait_queue_priority);
50
51void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
52{
53 unsigned long flags;
54
55 spin_lock_irqsave(&wq_head->lock, flags);
56 __remove_wait_queue(wq_head, wq_entry);
57 spin_unlock_irqrestore(&wq_head->lock, flags);
58}
59EXPORT_SYMBOL(remove_wait_queue);
60
61/*
62 * Scan threshold to break wait queue walk.
63 * This allows a waker to take a break from holding the
64 * wait queue lock during the wait queue walk.
65 */
66#define WAITQUEUE_WALK_BREAK_CNT 64
67
68/*
69 * The core wakeup function. Non-exclusive wakeups (nr_exclusive == 0) just
70 * wake everything up. If it's an exclusive wakeup (nr_exclusive == small +ve
71 * number) then we wake that number of exclusive tasks, and potentially all
72 * the non-exclusive tasks. Normally, exclusive tasks will be at the end of
73 * the list and any non-exclusive tasks will be woken first. A priority task
74 * may be at the head of the list, and can consume the event without any other
75 * tasks being woken.
76 *
77 * There are circumstances in which we can try to wake a task which has already
78 * started to run but is not in state TASK_RUNNING. try_to_wake_up() returns
79 * zero in this (rare) case, and we handle it by continuing to scan the queue.
80 */
81static int __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode,
82 int nr_exclusive, int wake_flags, void *key,
83 wait_queue_entry_t *bookmark)
84{
85 wait_queue_entry_t *curr, *next;
86 int cnt = 0;
87
88 lockdep_assert_held(&wq_head->lock);
89
90 if (bookmark && (bookmark->flags & WQ_FLAG_BOOKMARK)) {
91 curr = list_next_entry(bookmark, entry);
92
93 list_del(&bookmark->entry);
94 bookmark->flags = 0;
95 } else
96 curr = list_first_entry(&wq_head->head, wait_queue_entry_t, entry);
97
98 if (&curr->entry == &wq_head->head)
99 return nr_exclusive;
100
101 list_for_each_entry_safe_from(curr, next, &wq_head->head, entry) {
102 unsigned flags = curr->flags;
103 int ret;
104
105 if (flags & WQ_FLAG_BOOKMARK)
106 continue;
107
108 ret = curr->func(curr, mode, wake_flags, key);
109 if (ret < 0)
110 break;
111 if (ret && (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
112 break;
113
114 if (bookmark && (++cnt > WAITQUEUE_WALK_BREAK_CNT) &&
115 (&next->entry != &wq_head->head)) {
116 bookmark->flags = WQ_FLAG_BOOKMARK;
117 list_add_tail(&bookmark->entry, &next->entry);
118 break;
119 }
120 }
121
122 return nr_exclusive;
123}
124
125static void __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int mode,
126 int nr_exclusive, int wake_flags, void *key)
127{
128 unsigned long flags;
129 wait_queue_entry_t bookmark;
130
131 bookmark.flags = 0;
132 bookmark.private = NULL;
133 bookmark.func = NULL;
134 INIT_LIST_HEAD(&bookmark.entry);
135
136 do {
137 spin_lock_irqsave(&wq_head->lock, flags);
138 nr_exclusive = __wake_up_common(wq_head, mode, nr_exclusive,
139 wake_flags, key, &bookmark);
140 spin_unlock_irqrestore(&wq_head->lock, flags);
141 } while (bookmark.flags & WQ_FLAG_BOOKMARK);
142}
143
144/**
145 * __wake_up - wake up threads blocked on a waitqueue.
146 * @wq_head: the waitqueue
147 * @mode: which threads
148 * @nr_exclusive: how many wake-one or wake-many threads to wake up
149 * @key: is directly passed to the wakeup function
150 *
151 * If this function wakes up a task, it executes a full memory barrier before
152 * accessing the task state.
153 */
154void __wake_up(struct wait_queue_head *wq_head, unsigned int mode,
155 int nr_exclusive, void *key)
156{
157 __wake_up_common_lock(wq_head, mode, nr_exclusive, 0, key);
158}
159EXPORT_SYMBOL(__wake_up);
160
161/*
162 * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
163 */
164void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr)
165{
166 __wake_up_common(wq_head, mode, nr, 0, NULL, NULL);
167}
168EXPORT_SYMBOL_GPL(__wake_up_locked);
169
170void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key)
171{
172 __wake_up_common(wq_head, mode, 1, 0, key, NULL);
173}
174EXPORT_SYMBOL_GPL(__wake_up_locked_key);
175
176void __wake_up_locked_key_bookmark(struct wait_queue_head *wq_head,
177 unsigned int mode, void *key, wait_queue_entry_t *bookmark)
178{
179 __wake_up_common(wq_head, mode, 1, 0, key, bookmark);
180}
181EXPORT_SYMBOL_GPL(__wake_up_locked_key_bookmark);
182
183/**
184 * __wake_up_sync_key - wake up threads blocked on a waitqueue.
185 * @wq_head: the waitqueue
186 * @mode: which threads
187 * @key: opaque value to be passed to wakeup targets
188 *
189 * The sync wakeup differs that the waker knows that it will schedule
190 * away soon, so while the target thread will be woken up, it will not
191 * be migrated to another CPU - ie. the two threads are 'synchronized'
192 * with each other. This can prevent needless bouncing between CPUs.
193 *
194 * On UP it can prevent extra preemption.
195 *
196 * If this function wakes up a task, it executes a full memory barrier before
197 * accessing the task state.
198 */
199void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode,
200 void *key)
201{
202 if (unlikely(!wq_head))
203 return;
204
205 __wake_up_common_lock(wq_head, mode, 1, WF_SYNC, key);
206}
207EXPORT_SYMBOL_GPL(__wake_up_sync_key);
208
209/**
210 * __wake_up_locked_sync_key - wake up a thread blocked on a locked waitqueue.
211 * @wq_head: the waitqueue
212 * @mode: which threads
213 * @key: opaque value to be passed to wakeup targets
214 *
215 * The sync wakeup differs in that the waker knows that it will schedule
216 * away soon, so while the target thread will be woken up, it will not
217 * be migrated to another CPU - ie. the two threads are 'synchronized'
218 * with each other. This can prevent needless bouncing between CPUs.
219 *
220 * On UP it can prevent extra preemption.
221 *
222 * If this function wakes up a task, it executes a full memory barrier before
223 * accessing the task state.
224 */
225void __wake_up_locked_sync_key(struct wait_queue_head *wq_head,
226 unsigned int mode, void *key)
227{
228 __wake_up_common(wq_head, mode, 1, WF_SYNC, key, NULL);
229}
230EXPORT_SYMBOL_GPL(__wake_up_locked_sync_key);
231
232/*
233 * __wake_up_sync - see __wake_up_sync_key()
234 */
235void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode)
236{
237 __wake_up_sync_key(wq_head, mode, NULL);
238}
239EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */
240
241/*
242 * Note: we use "set_current_state()" _after_ the wait-queue add,
243 * because we need a memory barrier there on SMP, so that any
244 * wake-function that tests for the wait-queue being active
245 * will be guaranteed to see waitqueue addition _or_ subsequent
246 * tests in this thread will see the wakeup having taken place.
247 *
248 * The spin_unlock() itself is semi-permeable and only protects
249 * one way (it only protects stuff inside the critical region and
250 * stops them from bleeding out - it would still allow subsequent
251 * loads to move into the critical region).
252 */
253void
254prepare_to_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
255{
256 unsigned long flags;
257
258 wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
259 spin_lock_irqsave(&wq_head->lock, flags);
260 if (list_empty(&wq_entry->entry))
261 __add_wait_queue(wq_head, wq_entry);
262 set_current_state(state);
263 spin_unlock_irqrestore(&wq_head->lock, flags);
264}
265EXPORT_SYMBOL(prepare_to_wait);
266
267/* Returns true if we are the first waiter in the queue, false otherwise. */
268bool
269prepare_to_wait_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
270{
271 unsigned long flags;
272 bool was_empty = false;
273
274 wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
275 spin_lock_irqsave(&wq_head->lock, flags);
276 if (list_empty(&wq_entry->entry)) {
277 was_empty = list_empty(&wq_head->head);
278 __add_wait_queue_entry_tail(wq_head, wq_entry);
279 }
280 set_current_state(state);
281 spin_unlock_irqrestore(&wq_head->lock, flags);
282 return was_empty;
283}
284EXPORT_SYMBOL(prepare_to_wait_exclusive);
285
286void init_wait_entry(struct wait_queue_entry *wq_entry, int flags)
287{
288 wq_entry->flags = flags;
289 wq_entry->private = current;
290 wq_entry->func = autoremove_wake_function;
291 INIT_LIST_HEAD(&wq_entry->entry);
292}
293EXPORT_SYMBOL(init_wait_entry);
294
295long prepare_to_wait_event(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
296{
297 unsigned long flags;
298 long ret = 0;
299
300 spin_lock_irqsave(&wq_head->lock, flags);
301 if (signal_pending_state(state, current)) {
302 /*
303 * Exclusive waiter must not fail if it was selected by wakeup,
304 * it should "consume" the condition we were waiting for.
305 *
306 * The caller will recheck the condition and return success if
307 * we were already woken up, we can not miss the event because
308 * wakeup locks/unlocks the same wq_head->lock.
309 *
310 * But we need to ensure that set-condition + wakeup after that
311 * can't see us, it should wake up another exclusive waiter if
312 * we fail.
313 */
314 list_del_init(&wq_entry->entry);
315 ret = -ERESTARTSYS;
316 } else {
317 if (list_empty(&wq_entry->entry)) {
318 if (wq_entry->flags & WQ_FLAG_EXCLUSIVE)
319 __add_wait_queue_entry_tail(wq_head, wq_entry);
320 else
321 __add_wait_queue(wq_head, wq_entry);
322 }
323 set_current_state(state);
324 }
325 spin_unlock_irqrestore(&wq_head->lock, flags);
326
327 return ret;
328}
329EXPORT_SYMBOL(prepare_to_wait_event);
330
331/*
332 * Note! These two wait functions are entered with the
333 * wait-queue lock held (and interrupts off in the _irq
334 * case), so there is no race with testing the wakeup
335 * condition in the caller before they add the wait
336 * entry to the wake queue.
337 */
338int do_wait_intr(wait_queue_head_t *wq, wait_queue_entry_t *wait)
339{
340 if (likely(list_empty(&wait->entry)))
341 __add_wait_queue_entry_tail(wq, wait);
342
343 set_current_state(TASK_INTERRUPTIBLE);
344 if (signal_pending(current))
345 return -ERESTARTSYS;
346
347 spin_unlock(&wq->lock);
348 schedule();
349 spin_lock(&wq->lock);
350
351 return 0;
352}
353EXPORT_SYMBOL(do_wait_intr);
354
355int do_wait_intr_irq(wait_queue_head_t *wq, wait_queue_entry_t *wait)
356{
357 if (likely(list_empty(&wait->entry)))
358 __add_wait_queue_entry_tail(wq, wait);
359
360 set_current_state(TASK_INTERRUPTIBLE);
361 if (signal_pending(current))
362 return -ERESTARTSYS;
363
364 spin_unlock_irq(&wq->lock);
365 schedule();
366 spin_lock_irq(&wq->lock);
367
368 return 0;
369}
370EXPORT_SYMBOL(do_wait_intr_irq);
371
372/**
373 * finish_wait - clean up after waiting in a queue
374 * @wq_head: waitqueue waited on
375 * @wq_entry: wait descriptor
376 *
377 * Sets current thread back to running state and removes
378 * the wait descriptor from the given waitqueue if still
379 * queued.
380 */
381void finish_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
382{
383 unsigned long flags;
384
385 __set_current_state(TASK_RUNNING);
386 /*
387 * We can check for list emptiness outside the lock
388 * IFF:
389 * - we use the "careful" check that verifies both
390 * the next and prev pointers, so that there cannot
391 * be any half-pending updates in progress on other
392 * CPU's that we haven't seen yet (and that might
393 * still change the stack area.
394 * and
395 * - all other users take the lock (ie we can only
396 * have _one_ other CPU that looks at or modifies
397 * the list).
398 */
399 if (!list_empty_careful(&wq_entry->entry)) {
400 spin_lock_irqsave(&wq_head->lock, flags);
401 list_del_init(&wq_entry->entry);
402 spin_unlock_irqrestore(&wq_head->lock, flags);
403 }
404}
405EXPORT_SYMBOL(finish_wait);
406
407int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
408{
409 int ret = default_wake_function(wq_entry, mode, sync, key);
410
411 if (ret)
412 list_del_init_careful(&wq_entry->entry);
413
414 return ret;
415}
416EXPORT_SYMBOL(autoremove_wake_function);
417
418static inline bool is_kthread_should_stop(void)
419{
420 return (current->flags & PF_KTHREAD) && kthread_should_stop();
421}
422
423/*
424 * DEFINE_WAIT_FUNC(wait, woken_wake_func);
425 *
426 * add_wait_queue(&wq_head, &wait);
427 * for (;;) {
428 * if (condition)
429 * break;
430 *
431 * // in wait_woken() // in woken_wake_function()
432 *
433 * p->state = mode; wq_entry->flags |= WQ_FLAG_WOKEN;
434 * smp_mb(); // A try_to_wake_up():
435 * if (!(wq_entry->flags & WQ_FLAG_WOKEN)) <full barrier>
436 * schedule() if (p->state & mode)
437 * p->state = TASK_RUNNING; p->state = TASK_RUNNING;
438 * wq_entry->flags &= ~WQ_FLAG_WOKEN; ~~~~~~~~~~~~~~~~~~
439 * smp_mb(); // B condition = true;
440 * } smp_mb(); // C
441 * remove_wait_queue(&wq_head, &wait); wq_entry->flags |= WQ_FLAG_WOKEN;
442 */
443long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout)
444{
445 /*
446 * The below executes an smp_mb(), which matches with the full barrier
447 * executed by the try_to_wake_up() in woken_wake_function() such that
448 * either we see the store to wq_entry->flags in woken_wake_function()
449 * or woken_wake_function() sees our store to current->state.
450 */
451 set_current_state(mode); /* A */
452 if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
453 timeout = schedule_timeout(timeout);
454 __set_current_state(TASK_RUNNING);
455
456 /*
457 * The below executes an smp_mb(), which matches with the smp_mb() (C)
458 * in woken_wake_function() such that either we see the wait condition
459 * being true or the store to wq_entry->flags in woken_wake_function()
460 * follows ours in the coherence order.
461 */
462 smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */
463
464 return timeout;
465}
466EXPORT_SYMBOL(wait_woken);
467
468int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
469{
470 /* Pairs with the smp_store_mb() in wait_woken(). */
471 smp_mb(); /* C */
472 wq_entry->flags |= WQ_FLAG_WOKEN;
473
474 return default_wake_function(wq_entry, mode, sync, key);
475}
476EXPORT_SYMBOL(woken_wake_function);
1/*
2 * Generic waiting primitives.
3 *
4 * (C) 2004 Nadia Yvette Chambers, Oracle
5 */
6#include "sched.h"
7
8void __init_waitqueue_head(struct wait_queue_head *wq_head, const char *name, struct lock_class_key *key)
9{
10 spin_lock_init(&wq_head->lock);
11 lockdep_set_class_and_name(&wq_head->lock, key, name);
12 INIT_LIST_HEAD(&wq_head->head);
13}
14
15EXPORT_SYMBOL(__init_waitqueue_head);
16
17void add_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
18{
19 unsigned long flags;
20
21 wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
22 spin_lock_irqsave(&wq_head->lock, flags);
23 __add_wait_queue(wq_head, wq_entry);
24 spin_unlock_irqrestore(&wq_head->lock, flags);
25}
26EXPORT_SYMBOL(add_wait_queue);
27
28void add_wait_queue_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
29{
30 unsigned long flags;
31
32 wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
33 spin_lock_irqsave(&wq_head->lock, flags);
34 __add_wait_queue_entry_tail(wq_head, wq_entry);
35 spin_unlock_irqrestore(&wq_head->lock, flags);
36}
37EXPORT_SYMBOL(add_wait_queue_exclusive);
38
39void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
40{
41 unsigned long flags;
42
43 spin_lock_irqsave(&wq_head->lock, flags);
44 __remove_wait_queue(wq_head, wq_entry);
45 spin_unlock_irqrestore(&wq_head->lock, flags);
46}
47EXPORT_SYMBOL(remove_wait_queue);
48
49/*
50 * Scan threshold to break wait queue walk.
51 * This allows a waker to take a break from holding the
52 * wait queue lock during the wait queue walk.
53 */
54#define WAITQUEUE_WALK_BREAK_CNT 64
55
56/*
57 * The core wakeup function. Non-exclusive wakeups (nr_exclusive == 0) just
58 * wake everything up. If it's an exclusive wakeup (nr_exclusive == small +ve
59 * number) then we wake all the non-exclusive tasks and one exclusive task.
60 *
61 * There are circumstances in which we can try to wake a task which has already
62 * started to run but is not in state TASK_RUNNING. try_to_wake_up() returns
63 * zero in this (rare) case, and we handle it by continuing to scan the queue.
64 */
65static int __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode,
66 int nr_exclusive, int wake_flags, void *key,
67 wait_queue_entry_t *bookmark)
68{
69 wait_queue_entry_t *curr, *next;
70 int cnt = 0;
71
72 if (bookmark && (bookmark->flags & WQ_FLAG_BOOKMARK)) {
73 curr = list_next_entry(bookmark, entry);
74
75 list_del(&bookmark->entry);
76 bookmark->flags = 0;
77 } else
78 curr = list_first_entry(&wq_head->head, wait_queue_entry_t, entry);
79
80 if (&curr->entry == &wq_head->head)
81 return nr_exclusive;
82
83 list_for_each_entry_safe_from(curr, next, &wq_head->head, entry) {
84 unsigned flags = curr->flags;
85 int ret;
86
87 if (flags & WQ_FLAG_BOOKMARK)
88 continue;
89
90 ret = curr->func(curr, mode, wake_flags, key);
91 if (ret < 0)
92 break;
93 if (ret && (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
94 break;
95
96 if (bookmark && (++cnt > WAITQUEUE_WALK_BREAK_CNT) &&
97 (&next->entry != &wq_head->head)) {
98 bookmark->flags = WQ_FLAG_BOOKMARK;
99 list_add_tail(&bookmark->entry, &next->entry);
100 break;
101 }
102 }
103
104 return nr_exclusive;
105}
106
107static void __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int mode,
108 int nr_exclusive, int wake_flags, void *key)
109{
110 unsigned long flags;
111 wait_queue_entry_t bookmark;
112
113 bookmark.flags = 0;
114 bookmark.private = NULL;
115 bookmark.func = NULL;
116 INIT_LIST_HEAD(&bookmark.entry);
117
118 spin_lock_irqsave(&wq_head->lock, flags);
119 nr_exclusive = __wake_up_common(wq_head, mode, nr_exclusive, wake_flags, key, &bookmark);
120 spin_unlock_irqrestore(&wq_head->lock, flags);
121
122 while (bookmark.flags & WQ_FLAG_BOOKMARK) {
123 spin_lock_irqsave(&wq_head->lock, flags);
124 nr_exclusive = __wake_up_common(wq_head, mode, nr_exclusive,
125 wake_flags, key, &bookmark);
126 spin_unlock_irqrestore(&wq_head->lock, flags);
127 }
128}
129
130/**
131 * __wake_up - wake up threads blocked on a waitqueue.
132 * @wq_head: the waitqueue
133 * @mode: which threads
134 * @nr_exclusive: how many wake-one or wake-many threads to wake up
135 * @key: is directly passed to the wakeup function
136 *
137 * It may be assumed that this function implies a write memory barrier before
138 * changing the task state if and only if any tasks are woken up.
139 */
140void __wake_up(struct wait_queue_head *wq_head, unsigned int mode,
141 int nr_exclusive, void *key)
142{
143 __wake_up_common_lock(wq_head, mode, nr_exclusive, 0, key);
144}
145EXPORT_SYMBOL(__wake_up);
146
147/*
148 * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
149 */
150void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr)
151{
152 __wake_up_common(wq_head, mode, nr, 0, NULL, NULL);
153}
154EXPORT_SYMBOL_GPL(__wake_up_locked);
155
156void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key)
157{
158 __wake_up_common(wq_head, mode, 1, 0, key, NULL);
159}
160EXPORT_SYMBOL_GPL(__wake_up_locked_key);
161
162void __wake_up_locked_key_bookmark(struct wait_queue_head *wq_head,
163 unsigned int mode, void *key, wait_queue_entry_t *bookmark)
164{
165 __wake_up_common(wq_head, mode, 1, 0, key, bookmark);
166}
167EXPORT_SYMBOL_GPL(__wake_up_locked_key_bookmark);
168
169/**
170 * __wake_up_sync_key - wake up threads blocked on a waitqueue.
171 * @wq_head: the waitqueue
172 * @mode: which threads
173 * @nr_exclusive: how many wake-one or wake-many threads to wake up
174 * @key: opaque value to be passed to wakeup targets
175 *
176 * The sync wakeup differs that the waker knows that it will schedule
177 * away soon, so while the target thread will be woken up, it will not
178 * be migrated to another CPU - ie. the two threads are 'synchronized'
179 * with each other. This can prevent needless bouncing between CPUs.
180 *
181 * On UP it can prevent extra preemption.
182 *
183 * It may be assumed that this function implies a write memory barrier before
184 * changing the task state if and only if any tasks are woken up.
185 */
186void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode,
187 int nr_exclusive, void *key)
188{
189 int wake_flags = 1; /* XXX WF_SYNC */
190
191 if (unlikely(!wq_head))
192 return;
193
194 if (unlikely(nr_exclusive != 1))
195 wake_flags = 0;
196
197 __wake_up_common_lock(wq_head, mode, nr_exclusive, wake_flags, key);
198}
199EXPORT_SYMBOL_GPL(__wake_up_sync_key);
200
201/*
202 * __wake_up_sync - see __wake_up_sync_key()
203 */
204void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode, int nr_exclusive)
205{
206 __wake_up_sync_key(wq_head, mode, nr_exclusive, NULL);
207}
208EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */
209
210/*
211 * Note: we use "set_current_state()" _after_ the wait-queue add,
212 * because we need a memory barrier there on SMP, so that any
213 * wake-function that tests for the wait-queue being active
214 * will be guaranteed to see waitqueue addition _or_ subsequent
215 * tests in this thread will see the wakeup having taken place.
216 *
217 * The spin_unlock() itself is semi-permeable and only protects
218 * one way (it only protects stuff inside the critical region and
219 * stops them from bleeding out - it would still allow subsequent
220 * loads to move into the critical region).
221 */
222void
223prepare_to_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
224{
225 unsigned long flags;
226
227 wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
228 spin_lock_irqsave(&wq_head->lock, flags);
229 if (list_empty(&wq_entry->entry))
230 __add_wait_queue(wq_head, wq_entry);
231 set_current_state(state);
232 spin_unlock_irqrestore(&wq_head->lock, flags);
233}
234EXPORT_SYMBOL(prepare_to_wait);
235
236void
237prepare_to_wait_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
238{
239 unsigned long flags;
240
241 wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
242 spin_lock_irqsave(&wq_head->lock, flags);
243 if (list_empty(&wq_entry->entry))
244 __add_wait_queue_entry_tail(wq_head, wq_entry);
245 set_current_state(state);
246 spin_unlock_irqrestore(&wq_head->lock, flags);
247}
248EXPORT_SYMBOL(prepare_to_wait_exclusive);
249
250void init_wait_entry(struct wait_queue_entry *wq_entry, int flags)
251{
252 wq_entry->flags = flags;
253 wq_entry->private = current;
254 wq_entry->func = autoremove_wake_function;
255 INIT_LIST_HEAD(&wq_entry->entry);
256}
257EXPORT_SYMBOL(init_wait_entry);
258
259long prepare_to_wait_event(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
260{
261 unsigned long flags;
262 long ret = 0;
263
264 spin_lock_irqsave(&wq_head->lock, flags);
265 if (unlikely(signal_pending_state(state, current))) {
266 /*
267 * Exclusive waiter must not fail if it was selected by wakeup,
268 * it should "consume" the condition we were waiting for.
269 *
270 * The caller will recheck the condition and return success if
271 * we were already woken up, we can not miss the event because
272 * wakeup locks/unlocks the same wq_head->lock.
273 *
274 * But we need to ensure that set-condition + wakeup after that
275 * can't see us, it should wake up another exclusive waiter if
276 * we fail.
277 */
278 list_del_init(&wq_entry->entry);
279 ret = -ERESTARTSYS;
280 } else {
281 if (list_empty(&wq_entry->entry)) {
282 if (wq_entry->flags & WQ_FLAG_EXCLUSIVE)
283 __add_wait_queue_entry_tail(wq_head, wq_entry);
284 else
285 __add_wait_queue(wq_head, wq_entry);
286 }
287 set_current_state(state);
288 }
289 spin_unlock_irqrestore(&wq_head->lock, flags);
290
291 return ret;
292}
293EXPORT_SYMBOL(prepare_to_wait_event);
294
295/*
296 * Note! These two wait functions are entered with the
297 * wait-queue lock held (and interrupts off in the _irq
298 * case), so there is no race with testing the wakeup
299 * condition in the caller before they add the wait
300 * entry to the wake queue.
301 */
302int do_wait_intr(wait_queue_head_t *wq, wait_queue_entry_t *wait)
303{
304 if (likely(list_empty(&wait->entry)))
305 __add_wait_queue_entry_tail(wq, wait);
306
307 set_current_state(TASK_INTERRUPTIBLE);
308 if (signal_pending(current))
309 return -ERESTARTSYS;
310
311 spin_unlock(&wq->lock);
312 schedule();
313 spin_lock(&wq->lock);
314
315 return 0;
316}
317EXPORT_SYMBOL(do_wait_intr);
318
319int do_wait_intr_irq(wait_queue_head_t *wq, wait_queue_entry_t *wait)
320{
321 if (likely(list_empty(&wait->entry)))
322 __add_wait_queue_entry_tail(wq, wait);
323
324 set_current_state(TASK_INTERRUPTIBLE);
325 if (signal_pending(current))
326 return -ERESTARTSYS;
327
328 spin_unlock_irq(&wq->lock);
329 schedule();
330 spin_lock_irq(&wq->lock);
331
332 return 0;
333}
334EXPORT_SYMBOL(do_wait_intr_irq);
335
336/**
337 * finish_wait - clean up after waiting in a queue
338 * @wq_head: waitqueue waited on
339 * @wq_entry: wait descriptor
340 *
341 * Sets current thread back to running state and removes
342 * the wait descriptor from the given waitqueue if still
343 * queued.
344 */
345void finish_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
346{
347 unsigned long flags;
348
349 __set_current_state(TASK_RUNNING);
350 /*
351 * We can check for list emptiness outside the lock
352 * IFF:
353 * - we use the "careful" check that verifies both
354 * the next and prev pointers, so that there cannot
355 * be any half-pending updates in progress on other
356 * CPU's that we haven't seen yet (and that might
357 * still change the stack area.
358 * and
359 * - all other users take the lock (ie we can only
360 * have _one_ other CPU that looks at or modifies
361 * the list).
362 */
363 if (!list_empty_careful(&wq_entry->entry)) {
364 spin_lock_irqsave(&wq_head->lock, flags);
365 list_del_init(&wq_entry->entry);
366 spin_unlock_irqrestore(&wq_head->lock, flags);
367 }
368}
369EXPORT_SYMBOL(finish_wait);
370
371int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
372{
373 int ret = default_wake_function(wq_entry, mode, sync, key);
374
375 if (ret)
376 list_del_init(&wq_entry->entry);
377
378 return ret;
379}
380EXPORT_SYMBOL(autoremove_wake_function);
381
382static inline bool is_kthread_should_stop(void)
383{
384 return (current->flags & PF_KTHREAD) && kthread_should_stop();
385}
386
387/*
388 * DEFINE_WAIT_FUNC(wait, woken_wake_func);
389 *
390 * add_wait_queue(&wq_head, &wait);
391 * for (;;) {
392 * if (condition)
393 * break;
394 *
395 * p->state = mode; condition = true;
396 * smp_mb(); // A smp_wmb(); // C
397 * if (!wq_entry->flags & WQ_FLAG_WOKEN) wq_entry->flags |= WQ_FLAG_WOKEN;
398 * schedule() try_to_wake_up();
399 * p->state = TASK_RUNNING; ~~~~~~~~~~~~~~~~~~
400 * wq_entry->flags &= ~WQ_FLAG_WOKEN; condition = true;
401 * smp_mb() // B smp_wmb(); // C
402 * wq_entry->flags |= WQ_FLAG_WOKEN;
403 * }
404 * remove_wait_queue(&wq_head, &wait);
405 *
406 */
407long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout)
408{
409 set_current_state(mode); /* A */
410 /*
411 * The above implies an smp_mb(), which matches with the smp_wmb() from
412 * woken_wake_function() such that if we observe WQ_FLAG_WOKEN we must
413 * also observe all state before the wakeup.
414 */
415 if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
416 timeout = schedule_timeout(timeout);
417 __set_current_state(TASK_RUNNING);
418
419 /*
420 * The below implies an smp_mb(), it too pairs with the smp_wmb() from
421 * woken_wake_function() such that we must either observe the wait
422 * condition being true _OR_ WQ_FLAG_WOKEN such that we will not miss
423 * an event.
424 */
425 smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */
426
427 return timeout;
428}
429EXPORT_SYMBOL(wait_woken);
430
431int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
432{
433 /*
434 * Although this function is called under waitqueue lock, LOCK
435 * doesn't imply write barrier and the users expects write
436 * barrier semantics on wakeup functions. The following
437 * smp_wmb() is equivalent to smp_wmb() in try_to_wake_up()
438 * and is paired with smp_store_mb() in wait_woken().
439 */
440 smp_wmb(); /* C */
441 wq_entry->flags |= WQ_FLAG_WOKEN;
442
443 return default_wake_function(wq_entry, mode, sync, key);
444}
445EXPORT_SYMBOL(woken_wake_function);