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