projects/linux·blob v5.8 · refs

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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 * @key: opaque value to be passed to wakeup targets
173 *
174 * The sync wakeup differs that the waker knows that it will schedule
175 * away soon, so while the target thread will be woken up, it will not
176 * be migrated to another CPU - ie. the two threads are 'synchronized'
177 * with each other. This can prevent needless bouncing between CPUs.
178 *
179 * On UP it can prevent extra preemption.
180 *
181 * If this function wakes up a task, it executes a full memory barrier before
182 * accessing the task state.
183 */
184void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode,
185 void *key)
186{
187 if (unlikely(!wq_head))
188 return;
189
190 __wake_up_common_lock(wq_head, mode, 1, WF_SYNC, key);
191}
192EXPORT_SYMBOL_GPL(__wake_up_sync_key);
193
194/**
195 * __wake_up_locked_sync_key - wake up a thread blocked on a locked waitqueue.
196 * @wq_head: the waitqueue
197 * @mode: which threads
198 * @key: opaque value to be passed to wakeup targets
199 *
200 * The sync wakeup differs in that the waker knows that it will schedule
201 * away soon, so while the target thread will be woken up, it will not
202 * be migrated to another CPU - ie. the two threads are 'synchronized'
203 * with each other. This can prevent needless bouncing between CPUs.
204 *
205 * On UP it can prevent extra preemption.
206 *
207 * If this function wakes up a task, it executes a full memory barrier before
208 * accessing the task state.
209 */
210void __wake_up_locked_sync_key(struct wait_queue_head *wq_head,
211 unsigned int mode, void *key)
212{
213 __wake_up_common(wq_head, mode, 1, WF_SYNC, key, NULL);
214}
215EXPORT_SYMBOL_GPL(__wake_up_locked_sync_key);
216
217/*
218 * __wake_up_sync - see __wake_up_sync_key()
219 */
220void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode)
221{
222 __wake_up_sync_key(wq_head, mode, NULL);
223}
224EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */
225
226/*
227 * Note: we use "set_current_state()" _after_ the wait-queue add,
228 * because we need a memory barrier there on SMP, so that any
229 * wake-function that tests for the wait-queue being active
230 * will be guaranteed to see waitqueue addition _or_ subsequent
231 * tests in this thread will see the wakeup having taken place.
232 *
233 * The spin_unlock() itself is semi-permeable and only protects
234 * one way (it only protects stuff inside the critical region and
235 * stops them from bleeding out - it would still allow subsequent
236 * loads to move into the critical region).
237 */
238void
239prepare_to_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
240{
241 unsigned long flags;
242
243 wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
244 spin_lock_irqsave(&wq_head->lock, flags);
245 if (list_empty(&wq_entry->entry))
246 __add_wait_queue(wq_head, wq_entry);
247 set_current_state(state);
248 spin_unlock_irqrestore(&wq_head->lock, flags);
249}
250EXPORT_SYMBOL(prepare_to_wait);
251
252void
253prepare_to_wait_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
254{
255 unsigned long flags;
256
257 wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
258 spin_lock_irqsave(&wq_head->lock, flags);
259 if (list_empty(&wq_entry->entry))
260 __add_wait_queue_entry_tail(wq_head, wq_entry);
261 set_current_state(state);
262 spin_unlock_irqrestore(&wq_head->lock, flags);
263}
264EXPORT_SYMBOL(prepare_to_wait_exclusive);
265
266void init_wait_entry(struct wait_queue_entry *wq_entry, int flags)
267{
268 wq_entry->flags = flags;
269 wq_entry->private = current;
270 wq_entry->func = autoremove_wake_function;
271 INIT_LIST_HEAD(&wq_entry->entry);
272}
273EXPORT_SYMBOL(init_wait_entry);
274
275long prepare_to_wait_event(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
276{
277 unsigned long flags;
278 long ret = 0;
279
280 spin_lock_irqsave(&wq_head->lock, flags);
281 if (signal_pending_state(state, current)) {
282 /*
283 * Exclusive waiter must not fail if it was selected by wakeup,
284 * it should "consume" the condition we were waiting for.
285 *
286 * The caller will recheck the condition and return success if
287 * we were already woken up, we can not miss the event because
288 * wakeup locks/unlocks the same wq_head->lock.
289 *
290 * But we need to ensure that set-condition + wakeup after that
291 * can't see us, it should wake up another exclusive waiter if
292 * we fail.
293 */
294 list_del_init(&wq_entry->entry);
295 ret = -ERESTARTSYS;
296 } else {
297 if (list_empty(&wq_entry->entry)) {
298 if (wq_entry->flags & WQ_FLAG_EXCLUSIVE)
299 __add_wait_queue_entry_tail(wq_head, wq_entry);
300 else
301 __add_wait_queue(wq_head, wq_entry);
302 }
303 set_current_state(state);
304 }
305 spin_unlock_irqrestore(&wq_head->lock, flags);
306
307 return ret;
308}
309EXPORT_SYMBOL(prepare_to_wait_event);
310
311/*
312 * Note! These two wait functions are entered with the
313 * wait-queue lock held (and interrupts off in the _irq
314 * case), so there is no race with testing the wakeup
315 * condition in the caller before they add the wait
316 * entry to the wake queue.
317 */
318int do_wait_intr(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(&wq->lock);
328 schedule();
329 spin_lock(&wq->lock);
330
331 return 0;
332}
333EXPORT_SYMBOL(do_wait_intr);
334
335int do_wait_intr_irq(wait_queue_head_t *wq, wait_queue_entry_t *wait)
336{
337 if (likely(list_empty(&wait->entry)))
338 __add_wait_queue_entry_tail(wq, wait);
339
340 set_current_state(TASK_INTERRUPTIBLE);
341 if (signal_pending(current))
342 return -ERESTARTSYS;
343
344 spin_unlock_irq(&wq->lock);
345 schedule();
346 spin_lock_irq(&wq->lock);
347
348 return 0;
349}
350EXPORT_SYMBOL(do_wait_intr_irq);
351
352/**
353 * finish_wait - clean up after waiting in a queue
354 * @wq_head: waitqueue waited on
355 * @wq_entry: wait descriptor
356 *
357 * Sets current thread back to running state and removes
358 * the wait descriptor from the given waitqueue if still
359 * queued.
360 */
361void finish_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
362{
363 unsigned long flags;
364
365 __set_current_state(TASK_RUNNING);
366 /*
367 * We can check for list emptiness outside the lock
368 * IFF:
369 * - we use the "careful" check that verifies both
370 * the next and prev pointers, so that there cannot
371 * be any half-pending updates in progress on other
372 * CPU's that we haven't seen yet (and that might
373 * still change the stack area.
374 * and
375 * - all other users take the lock (ie we can only
376 * have _one_ other CPU that looks at or modifies
377 * the list).
378 */
379 if (!list_empty_careful(&wq_entry->entry)) {
380 spin_lock_irqsave(&wq_head->lock, flags);
381 list_del_init(&wq_entry->entry);
382 spin_unlock_irqrestore(&wq_head->lock, flags);
383 }
384}
385EXPORT_SYMBOL(finish_wait);
386
387int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
388{
389 int ret = default_wake_function(wq_entry, mode, sync, key);
390
391 if (ret)
392 list_del_init(&wq_entry->entry);
393
394 return ret;
395}
396EXPORT_SYMBOL(autoremove_wake_function);
397
398static inline bool is_kthread_should_stop(void)
399{
400 return (current->flags & PF_KTHREAD) && kthread_should_stop();
401}
402
403/*
404 * DEFINE_WAIT_FUNC(wait, woken_wake_func);
405 *
406 * add_wait_queue(&wq_head, &wait);
407 * for (;;) {
408 * if (condition)
409 * break;
410 *
411 * // in wait_woken() // in woken_wake_function()
412 *
413 * p->state = mode; wq_entry->flags |= WQ_FLAG_WOKEN;
414 * smp_mb(); // A try_to_wake_up():
415 * if (!(wq_entry->flags & WQ_FLAG_WOKEN)) <full barrier>
416 * schedule() if (p->state & mode)
417 * p->state = TASK_RUNNING; p->state = TASK_RUNNING;
418 * wq_entry->flags &= ~WQ_FLAG_WOKEN; ~~~~~~~~~~~~~~~~~~
419 * smp_mb(); // B condition = true;
420 * } smp_mb(); // C
421 * remove_wait_queue(&wq_head, &wait); wq_entry->flags |= WQ_FLAG_WOKEN;
422 */
423long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout)
424{
425 /*
426 * The below executes an smp_mb(), which matches with the full barrier
427 * executed by the try_to_wake_up() in woken_wake_function() such that
428 * either we see the store to wq_entry->flags in woken_wake_function()
429 * or woken_wake_function() sees our store to current->state.
430 */
431 set_current_state(mode); /* A */
432 if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
433 timeout = schedule_timeout(timeout);
434 __set_current_state(TASK_RUNNING);
435
436 /*
437 * The below executes an smp_mb(), which matches with the smp_mb() (C)
438 * in woken_wake_function() such that either we see the wait condition
439 * being true or the store to wq_entry->flags in woken_wake_function()
440 * follows ours in the coherence order.
441 */
442 smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */
443
444 return timeout;
445}
446EXPORT_SYMBOL(wait_woken);
447
448int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
449{
450 /* Pairs with the smp_store_mb() in wait_woken(). */
451 smp_mb(); /* C */
452 wq_entry->flags |= WQ_FLAG_WOKEN;
453
454 return default_wake_function(wq_entry, mode, sync, key);
455}
456EXPORT_SYMBOL(woken_wake_function);