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