~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

TOMOYO Linux Cross Reference
Linux/kernel/sched/wait.c

Version: ~ [ linux-4.19-rc7 ] ~ [ linux-4.18.12 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.74 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.131 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.159 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.19.8 ] ~ [ linux-3.18.123 ] ~ [ linux-3.17.8 ] ~ [ linux-3.16.59 ] ~ [ linux-3.15.10 ] ~ [ linux-3.14.79 ] ~ [ linux-3.13.11 ] ~ [ linux-3.12.74 ] ~ [ linux-3.11.10 ] ~ [ linux-3.10.108 ] ~ [ linux-3.9.11 ] ~ [ linux-3.8.13 ] ~ [ linux-3.7.10 ] ~ [ linux-3.6.11 ] ~ [ linux-3.5.7 ] ~ [ linux-3.4.113 ] ~ [ linux-3.3.8 ] ~ [ linux-3.2.102 ] ~ [ linux-3.1.10 ] ~ [ linux-3.0.101 ] ~ [ linux-2.6.39.4 ] ~ [ linux-2.6.38.8 ] ~ [ linux-2.6.37.6 ] ~ [ linux-2.6.36.4 ] ~ [ linux-2.6.35.14 ] ~ [ linux-2.6.34.15 ] ~ [ linux-2.6.33.20 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.31.14 ] ~ [ linux-2.6.30.10 ] ~ [ linux-2.6.29.6 ] ~ [ linux-2.6.28.10 ] ~ [ linux-2.6.27.62 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.5 ] ~ [ policy-sample ] ~
Architecture: ~ [ i386 ] ~ [ alpha ] ~ [ m68k ] ~ [ mips ] ~ [ ppc ] ~ [ sparc ] ~ [ sparc64 ] ~

  1 /*
  2  * Generic waiting primitives.
  3  *
  4  * (C) 2004 Nadia Yvette Chambers, Oracle
  5  */
  6 #include "sched.h"
  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 remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
 40 {
 41         unsigned long flags;
 42 
 43         spin_lock_irqsave(&wq_head->lock, flags);
 44         __remove_wait_queue(wq_head, wq_entry);
 45         spin_unlock_irqrestore(&wq_head->lock, flags);
 46 }
 47 EXPORT_SYMBOL(remove_wait_queue);
 48 
 49 /*
 50  * Scan threshold to break wait queue walk.
 51  * This allows a waker to take a break from holding the
 52  * wait queue lock during the wait queue walk.
 53  */
 54 #define WAITQUEUE_WALK_BREAK_CNT 64
 55 
 56 /*
 57  * The core wakeup function. Non-exclusive wakeups (nr_exclusive == 0) just
 58  * wake everything up. If it's an exclusive wakeup (nr_exclusive == small +ve
 59  * number) then we wake all the non-exclusive tasks and one exclusive task.
 60  *
 61  * There are circumstances in which we can try to wake a task which has already
 62  * started to run but is not in state TASK_RUNNING. try_to_wake_up() returns
 63  * zero in this (rare) case, and we handle it by continuing to scan the queue.
 64  */
 65 static int __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode,
 66                         int nr_exclusive, int wake_flags, void *key,
 67                         wait_queue_entry_t *bookmark)
 68 {
 69         wait_queue_entry_t *curr, *next;
 70         int cnt = 0;
 71 
 72         lockdep_assert_held(&wq_head->lock);
 73 
 74         if (bookmark && (bookmark->flags & WQ_FLAG_BOOKMARK)) {
 75                 curr = list_next_entry(bookmark, entry);
 76 
 77                 list_del(&bookmark->entry);
 78                 bookmark->flags = 0;
 79         } else
 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                 if (flags & WQ_FLAG_BOOKMARK)
 90                         continue;
 91 
 92                 ret = curr->func(curr, mode, wake_flags, key);
 93                 if (ret < 0)
 94                         break;
 95                 if (ret && (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
 96                         break;
 97 
 98                 if (bookmark && (++cnt > WAITQUEUE_WALK_BREAK_CNT) &&
 99                                 (&next->entry != &wq_head->head)) {
100                         bookmark->flags = WQ_FLAG_BOOKMARK;
101                         list_add_tail(&bookmark->entry, &next->entry);
102                         break;
103                 }
104         }
105 
106         return nr_exclusive;
107 }
108 
109 static void __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int mode,
110                         int nr_exclusive, int wake_flags, void *key)
111 {
112         unsigned long flags;
113         wait_queue_entry_t bookmark;
114 
115         bookmark.flags = 0;
116         bookmark.private = NULL;
117         bookmark.func = NULL;
118         INIT_LIST_HEAD(&bookmark.entry);
119 
120         spin_lock_irqsave(&wq_head->lock, flags);
121         nr_exclusive = __wake_up_common(wq_head, mode, nr_exclusive, wake_flags, key, &bookmark);
122         spin_unlock_irqrestore(&wq_head->lock, flags);
123 
124         while (bookmark.flags & WQ_FLAG_BOOKMARK) {
125                 spin_lock_irqsave(&wq_head->lock, flags);
126                 nr_exclusive = __wake_up_common(wq_head, mode, nr_exclusive,
127                                                 wake_flags, key, &bookmark);
128                 spin_unlock_irqrestore(&wq_head->lock, flags);
129         }
130 }
131 
132 /**
133  * __wake_up - wake up threads blocked on a waitqueue.
134  * @wq_head: the waitqueue
135  * @mode: which threads
136  * @nr_exclusive: how many wake-one or wake-many threads to wake up
137  * @key: is directly passed to the wakeup function
138  *
139  * If this function wakes up a task, it executes a full memory barrier before
140  * accessing the task state.
141  */
142 void __wake_up(struct wait_queue_head *wq_head, unsigned int mode,
143                         int nr_exclusive, void *key)
144 {
145         __wake_up_common_lock(wq_head, mode, nr_exclusive, 0, key);
146 }
147 EXPORT_SYMBOL(__wake_up);
148 
149 /*
150  * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
151  */
152 void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr)
153 {
154         __wake_up_common(wq_head, mode, nr, 0, NULL, NULL);
155 }
156 EXPORT_SYMBOL_GPL(__wake_up_locked);
157 
158 void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key)
159 {
160         __wake_up_common(wq_head, mode, 1, 0, key, NULL);
161 }
162 EXPORT_SYMBOL_GPL(__wake_up_locked_key);
163 
164 void __wake_up_locked_key_bookmark(struct wait_queue_head *wq_head,
165                 unsigned int mode, void *key, wait_queue_entry_t *bookmark)
166 {
167         __wake_up_common(wq_head, mode, 1, 0, key, bookmark);
168 }
169 EXPORT_SYMBOL_GPL(__wake_up_locked_key_bookmark);
170 
171 /**
172  * __wake_up_sync_key - wake up threads blocked on a waitqueue.
173  * @wq_head: the waitqueue
174  * @mode: which threads
175  * @nr_exclusive: how many wake-one or wake-many threads to wake up
176  * @key: opaque value to be passed to wakeup targets
177  *
178  * The sync wakeup differs that the waker knows that it will schedule
179  * away soon, so while the target thread will be woken up, it will not
180  * be migrated to another CPU - ie. the two threads are 'synchronized'
181  * with each other. This can prevent needless bouncing between CPUs.
182  *
183  * On UP it can prevent extra preemption.
184  *
185  * If this function wakes up a task, it executes a full memory barrier before
186  * accessing the task state.
187  */
188 void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode,
189                         int nr_exclusive, void *key)
190 {
191         int wake_flags = 1; /* XXX WF_SYNC */
192 
193         if (unlikely(!wq_head))
194                 return;
195 
196         if (unlikely(nr_exclusive != 1))
197                 wake_flags = 0;
198 
199         __wake_up_common_lock(wq_head, mode, nr_exclusive, wake_flags, key);
200 }
201 EXPORT_SYMBOL_GPL(__wake_up_sync_key);
202 
203 /*
204  * __wake_up_sync - see __wake_up_sync_key()
205  */
206 void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode, int nr_exclusive)
207 {
208         __wake_up_sync_key(wq_head, mode, nr_exclusive, NULL);
209 }
210 EXPORT_SYMBOL_GPL(__wake_up_sync);      /* For internal use only */
211 
212 /*
213  * Note: we use "set_current_state()" _after_ the wait-queue add,
214  * because we need a memory barrier there on SMP, so that any
215  * wake-function that tests for the wait-queue being active
216  * will be guaranteed to see waitqueue addition _or_ subsequent
217  * tests in this thread will see the wakeup having taken place.
218  *
219  * The spin_unlock() itself is semi-permeable and only protects
220  * one way (it only protects stuff inside the critical region and
221  * stops them from bleeding out - it would still allow subsequent
222  * loads to move into the critical region).
223  */
224 void
225 prepare_to_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
226 {
227         unsigned long flags;
228 
229         wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
230         spin_lock_irqsave(&wq_head->lock, flags);
231         if (list_empty(&wq_entry->entry))
232                 __add_wait_queue(wq_head, wq_entry);
233         set_current_state(state);
234         spin_unlock_irqrestore(&wq_head->lock, flags);
235 }
236 EXPORT_SYMBOL(prepare_to_wait);
237 
238 void
239 prepare_to_wait_exclusive(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_entry_tail(wq_head, wq_entry);
247         set_current_state(state);
248         spin_unlock_irqrestore(&wq_head->lock, flags);
249 }
250 EXPORT_SYMBOL(prepare_to_wait_exclusive);
251 
252 void init_wait_entry(struct wait_queue_entry *wq_entry, int flags)
253 {
254         wq_entry->flags = flags;
255         wq_entry->private = current;
256         wq_entry->func = autoremove_wake_function;
257         INIT_LIST_HEAD(&wq_entry->entry);
258 }
259 EXPORT_SYMBOL(init_wait_entry);
260 
261 long prepare_to_wait_event(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
262 {
263         unsigned long flags;
264         long ret = 0;
265 
266         spin_lock_irqsave(&wq_head->lock, flags);
267         if (unlikely(signal_pending_state(state, current))) {
268                 /*
269                  * Exclusive waiter must not fail if it was selected by wakeup,
270                  * it should "consume" the condition we were waiting for.
271                  *
272                  * The caller will recheck the condition and return success if
273                  * we were already woken up, we can not miss the event because
274                  * wakeup locks/unlocks the same wq_head->lock.
275                  *
276                  * But we need to ensure that set-condition + wakeup after that
277                  * can't see us, it should wake up another exclusive waiter if
278                  * we fail.
279                  */
280                 list_del_init(&wq_entry->entry);
281                 ret = -ERESTARTSYS;
282         } else {
283                 if (list_empty(&wq_entry->entry)) {
284                         if (wq_entry->flags & WQ_FLAG_EXCLUSIVE)
285                                 __add_wait_queue_entry_tail(wq_head, wq_entry);
286                         else
287                                 __add_wait_queue(wq_head, wq_entry);
288                 }
289                 set_current_state(state);
290         }
291         spin_unlock_irqrestore(&wq_head->lock, flags);
292 
293         return ret;
294 }
295 EXPORT_SYMBOL(prepare_to_wait_event);
296 
297 /*
298  * Note! These two wait functions are entered with the
299  * wait-queue lock held (and interrupts off in the _irq
300  * case), so there is no race with testing the wakeup
301  * condition in the caller before they add the wait
302  * entry to the wake queue.
303  */
304 int do_wait_intr(wait_queue_head_t *wq, wait_queue_entry_t *wait)
305 {
306         if (likely(list_empty(&wait->entry)))
307                 __add_wait_queue_entry_tail(wq, wait);
308 
309         set_current_state(TASK_INTERRUPTIBLE);
310         if (signal_pending(current))
311                 return -ERESTARTSYS;
312 
313         spin_unlock(&wq->lock);
314         schedule();
315         spin_lock(&wq->lock);
316 
317         return 0;
318 }
319 EXPORT_SYMBOL(do_wait_intr);
320 
321 int do_wait_intr_irq(wait_queue_head_t *wq, wait_queue_entry_t *wait)
322 {
323         if (likely(list_empty(&wait->entry)))
324                 __add_wait_queue_entry_tail(wq, wait);
325 
326         set_current_state(TASK_INTERRUPTIBLE);
327         if (signal_pending(current))
328                 return -ERESTARTSYS;
329 
330         spin_unlock_irq(&wq->lock);
331         schedule();
332         spin_lock_irq(&wq->lock);
333 
334         return 0;
335 }
336 EXPORT_SYMBOL(do_wait_intr_irq);
337 
338 /**
339  * finish_wait - clean up after waiting in a queue
340  * @wq_head: waitqueue waited on
341  * @wq_entry: wait descriptor
342  *
343  * Sets current thread back to running state and removes
344  * the wait descriptor from the given waitqueue if still
345  * queued.
346  */
347 void finish_wait(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
348 {
349         unsigned long flags;
350 
351         __set_current_state(TASK_RUNNING);
352         /*
353          * We can check for list emptiness outside the lock
354          * IFF:
355          *  - we use the "careful" check that verifies both
356          *    the next and prev pointers, so that there cannot
357          *    be any half-pending updates in progress on other
358          *    CPU's that we haven't seen yet (and that might
359          *    still change the stack area.
360          * and
361          *  - all other users take the lock (ie we can only
362          *    have _one_ other CPU that looks at or modifies
363          *    the list).
364          */
365         if (!list_empty_careful(&wq_entry->entry)) {
366                 spin_lock_irqsave(&wq_head->lock, flags);
367                 list_del_init(&wq_entry->entry);
368                 spin_unlock_irqrestore(&wq_head->lock, flags);
369         }
370 }
371 EXPORT_SYMBOL(finish_wait);
372 
373 int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
374 {
375         int ret = default_wake_function(wq_entry, mode, sync, key);
376 
377         if (ret)
378                 list_del_init(&wq_entry->entry);
379 
380         return ret;
381 }
382 EXPORT_SYMBOL(autoremove_wake_function);
383 
384 static inline bool is_kthread_should_stop(void)
385 {
386         return (current->flags & PF_KTHREAD) && kthread_should_stop();
387 }
388 
389 /*
390  * DEFINE_WAIT_FUNC(wait, woken_wake_func);
391  *
392  * add_wait_queue(&wq_head, &wait);
393  * for (;;) {
394  *     if (condition)
395  *         break;
396  *
397  *     // in wait_woken()                       // in woken_wake_function()
398  *
399  *     p->state = mode;                         wq_entry->flags |= WQ_FLAG_WOKEN;
400  *     smp_mb(); // A                           try_to_wake_up():
401  *     if (!(wq_entry->flags & WQ_FLAG_WOKEN))     <full barrier>
402  *         schedule()                              if (p->state & mode)
403  *     p->state = TASK_RUNNING;                       p->state = TASK_RUNNING;
404  *     wq_entry->flags &= ~WQ_FLAG_WOKEN;       ~~~~~~~~~~~~~~~~~~
405  *     smp_mb(); // B                           condition = true;
406  * }                                            smp_mb(); // C
407  * remove_wait_queue(&wq_head, &wait);          wq_entry->flags |= WQ_FLAG_WOKEN;
408  */
409 long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout)
410 {
411         /*
412          * The below executes an smp_mb(), which matches with the full barrier
413          * executed by the try_to_wake_up() in woken_wake_function() such that
414          * either we see the store to wq_entry->flags in woken_wake_function()
415          * or woken_wake_function() sees our store to current->state.
416          */
417         set_current_state(mode); /* A */
418         if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
419                 timeout = schedule_timeout(timeout);
420         __set_current_state(TASK_RUNNING);
421 
422         /*
423          * The below executes an smp_mb(), which matches with the smp_mb() (C)
424          * in woken_wake_function() such that either we see the wait condition
425          * being true or the store to wq_entry->flags in woken_wake_function()
426          * follows ours in the coherence order.
427          */
428         smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */
429 
430         return timeout;
431 }
432 EXPORT_SYMBOL(wait_woken);
433 
434 int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
435 {
436         /* Pairs with the smp_store_mb() in wait_woken(). */
437         smp_mb(); /* C */
438         wq_entry->flags |= WQ_FLAG_WOKEN;
439 
440         return default_wake_function(wq_entry, mode, sync, key);
441 }
442 EXPORT_SYMBOL(woken_wake_function);
443 

~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

kernel.org | git.kernel.org | LWN.net | Project Home | Wiki (Japanese) | Wiki (English) | SVN repository | Mail admin

Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.

osdn.jp