Merge tag 'ext4_for_linus_stable' of git://git.kernel.org/pub/scm/linux/kernel/git...
[linux-2.6-microblaze.git] / kernel / sched / wait.c
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
9 void __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
16 EXPORT_SYMBOL(__init_waitqueue_head);
17
18 void 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 }
27 EXPORT_SYMBOL(add_wait_queue);
28
29 void 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 }
38 EXPORT_SYMBOL(add_wait_queue_exclusive);
39
40 void 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 }
49 EXPORT_SYMBOL_GPL(add_wait_queue_priority);
50
51 void 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 }
59 EXPORT_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  */
81 static 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
125 static 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  */
154 void __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 }
159 EXPORT_SYMBOL(__wake_up);
160
161 /*
162  * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
163  */
164 void __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 }
168 EXPORT_SYMBOL_GPL(__wake_up_locked);
169
170 void __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 }
174 EXPORT_SYMBOL_GPL(__wake_up_locked_key);
175
176 void __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 }
181 EXPORT_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  */
199 void __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 }
207 EXPORT_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  */
225 void __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 }
230 EXPORT_SYMBOL_GPL(__wake_up_locked_sync_key);
231
232 /*
233  * __wake_up_sync - see __wake_up_sync_key()
234  */
235 void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode)
236 {
237         __wake_up_sync_key(wq_head, mode, NULL);
238 }
239 EXPORT_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  */
253 void
254 prepare_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 }
265 EXPORT_SYMBOL(prepare_to_wait);
266
267 void
268 prepare_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 }
279 EXPORT_SYMBOL(prepare_to_wait_exclusive);
280
281 void 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 }
288 EXPORT_SYMBOL(init_wait_entry);
289
290 long 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 }
324 EXPORT_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  */
333 int 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 }
348 EXPORT_SYMBOL(do_wait_intr);
349
350 int 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 }
365 EXPORT_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  */
376 void 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 }
400 EXPORT_SYMBOL(finish_wait);
401
402 int 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 }
411 EXPORT_SYMBOL(autoremove_wake_function);
412
413 static 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  */
438 long 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 }
461 EXPORT_SYMBOL(wait_woken);
462
463 int 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 }
471 EXPORT_SYMBOL(woken_wake_function);