projects/linux·blob v5.13 · 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 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
267void
268prepare_to_wait_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
269{
270 unsigned long flags;
271
272 wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
273 spin_lock_irqsave(&wq_head->lock, flags);
274 if (list_empty(&wq_entry->entry))
275 __add_wait_queue_entry_tail(wq_head, wq_entry);
276 set_current_state(state);
277 spin_unlock_irqrestore(&wq_head->lock, flags);
278}
279EXPORT_SYMBOL(prepare_to_wait_exclusive);
280
281void init_wait_entry(struct wait_queue_entry *wq_entry, int flags)
282{
283 wq_entry->flags = flags;
284 wq_entry->private = current;
285 wq_entry->func = autoremove_wake_function;
286 INIT_LIST_HEAD(&wq_entry->entry);
287}
288EXPORT_SYMBOL(init_wait_entry);
289
290long prepare_to_wait_event(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
291{
292 unsigned long flags;
293 long ret = 0;
294
295 spin_lock_irqsave(&wq_head->lock, flags);
296 if (signal_pending_state(state, current)) {
297 /*
298 * Exclusive waiter must not fail if it was selected by wakeup,
299 * it should "consume" the condition we were waiting for.
300 *
301 * The caller will recheck the condition and return success if
302 * we were already woken up, we can not miss the event because
303 * wakeup locks/unlocks the same wq_head->lock.
304 *
305 * But we need to ensure that set-condition + wakeup after that
306 * can't see us, it should wake up another exclusive waiter if
307 * we fail.
308 */
309 list_del_init(&wq_entry->entry);
310 ret = -ERESTARTSYS;
311 } else {
312 if (list_empty(&wq_entry->entry)) {
313 if (wq_entry->flags & WQ_FLAG_EXCLUSIVE)
314 __add_wait_queue_entry_tail(wq_head, wq_entry);
315 else
316 __add_wait_queue(wq_head, wq_entry);
317 }
318 set_current_state(state);
319 }
320 spin_unlock_irqrestore(&wq_head->lock, flags);
321
322 return ret;
323}
324EXPORT_SYMBOL(prepare_to_wait_event);
325
326/*
327 * Note! These two wait functions are entered with the
328 * wait-queue lock held (and interrupts off in the _irq
329 * case), so there is no race with testing the wakeup
330 * condition in the caller before they add the wait
331 * entry to the wake queue.
332 */
333int do_wait_intr(wait_queue_head_t *wq, wait_queue_entry_t *wait)
334{
335 if (likely(list_empty(&wait->entry)))
336 __add_wait_queue_entry_tail(wq, wait);
337
338 set_current_state(TASK_INTERRUPTIBLE);
339 if (signal_pending(current))
340 return -ERESTARTSYS;
341
342 spin_unlock(&wq->lock);
343 schedule();
344 spin_lock(&wq->lock);
345
346 return 0;
347}
348EXPORT_SYMBOL(do_wait_intr);
349
350int do_wait_intr_irq(wait_queue_head_t *wq, wait_queue_entry_t *wait)
351{
352 if (likely(list_empty(&wait->entry)))
353 __add_wait_queue_entry_tail(wq, wait);
354
355 set_current_state(TASK_INTERRUPTIBLE);
356 if (signal_pending(current))
357 return -ERESTARTSYS;
358
359 spin_unlock_irq(&wq->lock);
360 schedule();
361 spin_lock_irq(&wq->lock);
362
363 return 0;
364}
365EXPORT_SYMBOL(do_wait_intr_irq);
366
367/**
368 * finish_wait - clean up after waiting in a queue
369 * @wq_head: waitqueue waited on
370 * @wq_entry: wait descriptor
371 *
372 * Sets current thread back to running state and removes
373 * the wait descriptor from the given waitqueue if still
374 * queued.
375 */
376void finish_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
377{
378 unsigned long flags;
379
380 __set_current_state(TASK_RUNNING);
381 /*
382 * We can check for list emptiness outside the lock
383 * IFF:
384 * - we use the "careful" check that verifies both
385 * the next and prev pointers, so that there cannot
386 * be any half-pending updates in progress on other
387 * CPU's that we haven't seen yet (and that might
388 * still change the stack area.
389 * and
390 * - all other users take the lock (ie we can only
391 * have _one_ other CPU that looks at or modifies
392 * the list).
393 */
394 if (!list_empty_careful(&wq_entry->entry)) {
395 spin_lock_irqsave(&wq_head->lock, flags);
396 list_del_init(&wq_entry->entry);
397 spin_unlock_irqrestore(&wq_head->lock, flags);
398 }
399}
400EXPORT_SYMBOL(finish_wait);
401
402int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
403{
404 int ret = default_wake_function(wq_entry, mode, sync, key);
405
406 if (ret)
407 list_del_init_careful(&wq_entry->entry);
408
409 return ret;
410}
411EXPORT_SYMBOL(autoremove_wake_function);
412
413static inline bool is_kthread_should_stop(void)
414{
415 return (current->flags & PF_KTHREAD) && kthread_should_stop();
416}
417
418/*
419 * DEFINE_WAIT_FUNC(wait, woken_wake_func);
420 *
421 * add_wait_queue(&wq_head, &wait);
422 * for (;;) {
423 * if (condition)
424 * break;
425 *
426 * // in wait_woken() // in woken_wake_function()
427 *
428 * p->state = mode; wq_entry->flags |= WQ_FLAG_WOKEN;
429 * smp_mb(); // A try_to_wake_up():
430 * if (!(wq_entry->flags & WQ_FLAG_WOKEN)) <full barrier>
431 * schedule() if (p->state & mode)
432 * p->state = TASK_RUNNING; p->state = TASK_RUNNING;
433 * wq_entry->flags &= ~WQ_FLAG_WOKEN; ~~~~~~~~~~~~~~~~~~
434 * smp_mb(); // B condition = true;
435 * } smp_mb(); // C
436 * remove_wait_queue(&wq_head, &wait); wq_entry->flags |= WQ_FLAG_WOKEN;
437 */
438long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout)
439{
440 /*
441 * The below executes an smp_mb(), which matches with the full barrier
442 * executed by the try_to_wake_up() in woken_wake_function() such that
443 * either we see the store to wq_entry->flags in woken_wake_function()
444 * or woken_wake_function() sees our store to current->state.
445 */
446 set_current_state(mode); /* A */
447 if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
448 timeout = schedule_timeout(timeout);
449 __set_current_state(TASK_RUNNING);
450
451 /*
452 * The below executes an smp_mb(), which matches with the smp_mb() (C)
453 * in woken_wake_function() such that either we see the wait condition
454 * being true or the store to wq_entry->flags in woken_wake_function()
455 * follows ours in the coherence order.
456 */
457 smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */
458
459 return timeout;
460}
461EXPORT_SYMBOL(wait_woken);
462
463int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
464{
465 /* Pairs with the smp_store_mb() in wait_woken(). */
466 smp_mb(); /* C */
467 wq_entry->flags |= WQ_FLAG_WOKEN;
468
469 return default_wake_function(wq_entry, mode, sync, key);
470}
471EXPORT_SYMBOL(woken_wake_function);