1/*
  2 * Generic waiting primitives.
  3 *
  4 * (C) 2004 Nadia Yvette Chambers, Oracle
  5 */
  6#include <linux/init.h>
  7#include <linux/export.h>
  8#include <linux/sched.h>
  9#include <linux/mm.h>
 10#include <linux/wait.h>
 11#include <linux/hash.h>
 12
 13void __init_waitqueue_head(wait_queue_head_t *q, const char *name, struct lock_class_key *key)
 14{
 15	spin_lock_init(&q->lock);
 16	lockdep_set_class_and_name(&q->lock, key, name);
 17	INIT_LIST_HEAD(&q->task_list);
 18}
 19
 20EXPORT_SYMBOL(__init_waitqueue_head);
 21
 22void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
 23{
 24	unsigned long flags;
 25
 26	wait->flags &= ~WQ_FLAG_EXCLUSIVE;
 27	spin_lock_irqsave(&q->lock, flags);
 28	__add_wait_queue(q, wait);
 29	spin_unlock_irqrestore(&q->lock, flags);
 30}
 31EXPORT_SYMBOL(add_wait_queue);
 32
 33void add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait)
 34{
 35	unsigned long flags;
 36
 37	wait->flags |= WQ_FLAG_EXCLUSIVE;
 38	spin_lock_irqsave(&q->lock, flags);
 39	__add_wait_queue_tail(q, wait);
 40	spin_unlock_irqrestore(&q->lock, flags);
 41}
 42EXPORT_SYMBOL(add_wait_queue_exclusive);
 43
 44void remove_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
 45{
 46	unsigned long flags;
 47
 48	spin_lock_irqsave(&q->lock, flags);
 49	__remove_wait_queue(q, wait);
 50	spin_unlock_irqrestore(&q->lock, flags);
 51}
 52EXPORT_SYMBOL(remove_wait_queue);
 53
 54
 55/*
 56 * The core wakeup function. Non-exclusive wakeups (nr_exclusive == 0) just
 57 * wake everything up. If it's an exclusive wakeup (nr_exclusive == small +ve
 58 * number) then we wake all the non-exclusive tasks and one exclusive task.
 59 *
 60 * There are circumstances in which we can try to wake a task which has already
 61 * started to run but is not in state TASK_RUNNING. try_to_wake_up() returns
 62 * zero in this (rare) case, and we handle it by continuing to scan the queue.
 63 */
 64static void __wake_up_common(wait_queue_head_t *q, unsigned int mode,
 65			int nr_exclusive, int wake_flags, void *key)
 66{
 67	wait_queue_t *curr, *next;
 68
 69	list_for_each_entry_safe(curr, next, &q->task_list, task_list) {
 70		unsigned flags = curr->flags;
 71
 72		if (curr->func(curr, mode, wake_flags, key) &&
 73				(flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
 74			break;
 75	}
 76}
 77
 78/**
 79 * __wake_up - wake up threads blocked on a waitqueue.
 80 * @q: the waitqueue
 81 * @mode: which threads
 82 * @nr_exclusive: how many wake-one or wake-many threads to wake up
 83 * @key: is directly passed to the wakeup function
 84 *
 85 * It may be assumed that this function implies a write memory barrier before
 86 * changing the task state if and only if any tasks are woken up.
 87 */
 88void __wake_up(wait_queue_head_t *q, unsigned int mode,
 89			int nr_exclusive, void *key)
 90{
 91	unsigned long flags;
 92
 93	spin_lock_irqsave(&q->lock, flags);
 94	__wake_up_common(q, mode, nr_exclusive, 0, key);
 95	spin_unlock_irqrestore(&q->lock, flags);
 96}
 97EXPORT_SYMBOL(__wake_up);
 98
 99/*
100 * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
101 */
102void __wake_up_locked(wait_queue_head_t *q, unsigned int mode, int nr)
103{
104	__wake_up_common(q, mode, nr, 0, NULL);
105}
106EXPORT_SYMBOL_GPL(__wake_up_locked);
107
108void __wake_up_locked_key(wait_queue_head_t *q, unsigned int mode, void *key)
109{
110	__wake_up_common(q, mode, 1, 0, key);
111}
112EXPORT_SYMBOL_GPL(__wake_up_locked_key);
113
114/**
115 * __wake_up_sync_key - wake up threads blocked on a waitqueue.
116 * @q: the waitqueue
117 * @mode: which threads
118 * @nr_exclusive: how many wake-one or wake-many threads to wake up
119 * @key: opaque value to be passed to wakeup targets
120 *
121 * The sync wakeup differs that the waker knows that it will schedule
122 * away soon, so while the target thread will be woken up, it will not
123 * be migrated to another CPU - ie. the two threads are 'synchronized'
124 * with each other. This can prevent needless bouncing between CPUs.
125 *
126 * On UP it can prevent extra preemption.
127 *
128 * It may be assumed that this function implies a write memory barrier before
129 * changing the task state if and only if any tasks are woken up.
130 */
131void __wake_up_sync_key(wait_queue_head_t *q, unsigned int mode,
132			int nr_exclusive, void *key)
133{
134	unsigned long flags;
135	int wake_flags = 1; /* XXX WF_SYNC */
136
137	if (unlikely(!q))
138		return;
139
140	if (unlikely(nr_exclusive != 1))
141		wake_flags = 0;
142
143	spin_lock_irqsave(&q->lock, flags);
144	__wake_up_common(q, mode, nr_exclusive, wake_flags, key);
145	spin_unlock_irqrestore(&q->lock, flags);
146}
147EXPORT_SYMBOL_GPL(__wake_up_sync_key);
148
149/*
150 * __wake_up_sync - see __wake_up_sync_key()
151 */
152void __wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr_exclusive)
153{
154	__wake_up_sync_key(q, mode, nr_exclusive, NULL);
155}
156EXPORT_SYMBOL_GPL(__wake_up_sync);	/* For internal use only */
157
158/*
159 * Note: we use "set_current_state()" _after_ the wait-queue add,
160 * because we need a memory barrier there on SMP, so that any
161 * wake-function that tests for the wait-queue being active
162 * will be guaranteed to see waitqueue addition _or_ subsequent
163 * tests in this thread will see the wakeup having taken place.
164 *
165 * The spin_unlock() itself is semi-permeable and only protects
166 * one way (it only protects stuff inside the critical region and
167 * stops them from bleeding out - it would still allow subsequent
168 * loads to move into the critical region).
169 */
170void
171prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, int state)
172{
173	unsigned long flags;
174
175	wait->flags &= ~WQ_FLAG_EXCLUSIVE;
176	spin_lock_irqsave(&q->lock, flags);
177	if (list_empty(&wait->task_list))
178		__add_wait_queue(q, wait);
179	set_current_state(state);
180	spin_unlock_irqrestore(&q->lock, flags);
181}
182EXPORT_SYMBOL(prepare_to_wait);
183
184void
185prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state)
186{
187	unsigned long flags;
188
189	wait->flags |= WQ_FLAG_EXCLUSIVE;
190	spin_lock_irqsave(&q->lock, flags);
191	if (list_empty(&wait->task_list))
192		__add_wait_queue_tail(q, wait);
193	set_current_state(state);
194	spin_unlock_irqrestore(&q->lock, flags);
195}
196EXPORT_SYMBOL(prepare_to_wait_exclusive);
197
198long prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int state)
199{
200	unsigned long flags;
201
202	if (signal_pending_state(state, current))
203		return -ERESTARTSYS;
204
205	wait->private = current;
206	wait->func = autoremove_wake_function;
207
208	spin_lock_irqsave(&q->lock, flags);
209	if (list_empty(&wait->task_list)) {
210		if (wait->flags & WQ_FLAG_EXCLUSIVE)
211			__add_wait_queue_tail(q, wait);
212		else
213			__add_wait_queue(q, wait);
214	}
215	set_current_state(state);
216	spin_unlock_irqrestore(&q->lock, flags);
217
218	return 0;
219}
220EXPORT_SYMBOL(prepare_to_wait_event);
221
222/**
223 * finish_wait - clean up after waiting in a queue
224 * @q: waitqueue waited on
225 * @wait: wait descriptor
226 *
227 * Sets current thread back to running state and removes
228 * the wait descriptor from the given waitqueue if still
229 * queued.
230 */
231void finish_wait(wait_queue_head_t *q, wait_queue_t *wait)
232{
233	unsigned long flags;
234
235	__set_current_state(TASK_RUNNING);
236	/*
237	 * We can check for list emptiness outside the lock
238	 * IFF:
239	 *  - we use the "careful" check that verifies both
240	 *    the next and prev pointers, so that there cannot
241	 *    be any half-pending updates in progress on other
242	 *    CPU's that we haven't seen yet (and that might
243	 *    still change the stack area.
244	 * and
245	 *  - all other users take the lock (ie we can only
246	 *    have _one_ other CPU that looks at or modifies
247	 *    the list).
248	 */
249	if (!list_empty_careful(&wait->task_list)) {
250		spin_lock_irqsave(&q->lock, flags);
251		list_del_init(&wait->task_list);
252		spin_unlock_irqrestore(&q->lock, flags);
253	}
254}
255EXPORT_SYMBOL(finish_wait);
256
257/**
258 * abort_exclusive_wait - abort exclusive waiting in a queue
259 * @q: waitqueue waited on
260 * @wait: wait descriptor
261 * @mode: runstate of the waiter to be woken
262 * @key: key to identify a wait bit queue or %NULL
263 *
264 * Sets current thread back to running state and removes
265 * the wait descriptor from the given waitqueue if still
266 * queued.
267 *
268 * Wakes up the next waiter if the caller is concurrently
269 * woken up through the queue.
270 *
271 * This prevents waiter starvation where an exclusive waiter
272 * aborts and is woken up concurrently and no one wakes up
273 * the next waiter.
274 */
275void abort_exclusive_wait(wait_queue_head_t *q, wait_queue_t *wait,
276			unsigned int mode, void *key)
277{
278	unsigned long flags;
279
280	__set_current_state(TASK_RUNNING);
281	spin_lock_irqsave(&q->lock, flags);
282	if (!list_empty(&wait->task_list))
283		list_del_init(&wait->task_list);
284	else if (waitqueue_active(q))
285		__wake_up_locked_key(q, mode, key);
286	spin_unlock_irqrestore(&q->lock, flags);
287}
288EXPORT_SYMBOL(abort_exclusive_wait);
289
290int autoremove_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
291{
292	int ret = default_wake_function(wait, mode, sync, key);
293
294	if (ret)
295		list_del_init(&wait->task_list);
296	return ret;
297}
298EXPORT_SYMBOL(autoremove_wake_function);
299
300int wake_bit_function(wait_queue_t *wait, unsigned mode, int sync, void *arg)
301{
302	struct wait_bit_key *key = arg;
303	struct wait_bit_queue *wait_bit
304		= container_of(wait, struct wait_bit_queue, wait);
305
306	if (wait_bit->key.flags != key->flags ||
307			wait_bit->key.bit_nr != key->bit_nr ||
308			test_bit(key->bit_nr, key->flags))
309		return 0;
310	else
311		return autoremove_wake_function(wait, mode, sync, key);
312}
313EXPORT_SYMBOL(wake_bit_function);
314
315/*
316 * To allow interruptible waiting and asynchronous (i.e. nonblocking)
317 * waiting, the actions of __wait_on_bit() and __wait_on_bit_lock() are
318 * permitted return codes. Nonzero return codes halt waiting and return.
319 */
320int __sched
321__wait_on_bit(wait_queue_head_t *wq, struct wait_bit_queue *q,
322			int (*action)(void *), unsigned mode)
323{
324	int ret = 0;
325
326	do {
327		prepare_to_wait(wq, &q->wait, mode);
328		if (test_bit(q->key.bit_nr, q->key.flags))
329			ret = (*action)(q->key.flags);
330	} while (test_bit(q->key.bit_nr, q->key.flags) && !ret);
331	finish_wait(wq, &q->wait);
332	return ret;
333}
334EXPORT_SYMBOL(__wait_on_bit);
335
336int __sched out_of_line_wait_on_bit(void *word, int bit,
337					int (*action)(void *), unsigned mode)
338{
339	wait_queue_head_t *wq = bit_waitqueue(word, bit);
340	DEFINE_WAIT_BIT(wait, word, bit);
341
342	return __wait_on_bit(wq, &wait, action, mode);
343}
344EXPORT_SYMBOL(out_of_line_wait_on_bit);
345
346int __sched
347__wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
348			int (*action)(void *), unsigned mode)
349{
350	do {
351		int ret;
352
353		prepare_to_wait_exclusive(wq, &q->wait, mode);
354		if (!test_bit(q->key.bit_nr, q->key.flags))
355			continue;
356		ret = action(q->key.flags);
357		if (!ret)
358			continue;
359		abort_exclusive_wait(wq, &q->wait, mode, &q->key);
360		return ret;
361	} while (test_and_set_bit(q->key.bit_nr, q->key.flags));
362	finish_wait(wq, &q->wait);
363	return 0;
364}
365EXPORT_SYMBOL(__wait_on_bit_lock);
366
367int __sched out_of_line_wait_on_bit_lock(void *word, int bit,
368					int (*action)(void *), unsigned mode)
369{
370	wait_queue_head_t *wq = bit_waitqueue(word, bit);
371	DEFINE_WAIT_BIT(wait, word, bit);
372
373	return __wait_on_bit_lock(wq, &wait, action, mode);
374}
375EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);
376
377void __wake_up_bit(wait_queue_head_t *wq, void *word, int bit)
378{
379	struct wait_bit_key key = __WAIT_BIT_KEY_INITIALIZER(word, bit);
380	if (waitqueue_active(wq))
381		__wake_up(wq, TASK_NORMAL, 1, &key);
382}
383EXPORT_SYMBOL(__wake_up_bit);
384
385/**
386 * wake_up_bit - wake up a waiter on a bit
387 * @word: the word being waited on, a kernel virtual address
388 * @bit: the bit of the word being waited on
389 *
390 * There is a standard hashed waitqueue table for generic use. This
391 * is the part of the hashtable's accessor API that wakes up waiters
392 * on a bit. For instance, if one were to have waiters on a bitflag,
393 * one would call wake_up_bit() after clearing the bit.
394 *
395 * In order for this to function properly, as it uses waitqueue_active()
396 * internally, some kind of memory barrier must be done prior to calling
397 * this. Typically, this will be smp_mb__after_clear_bit(), but in some
398 * cases where bitflags are manipulated non-atomically under a lock, one
399 * may need to use a less regular barrier, such fs/inode.c's smp_mb(),
400 * because spin_unlock() does not guarantee a memory barrier.
401 */
402void wake_up_bit(void *word, int bit)
403{
404	__wake_up_bit(bit_waitqueue(word, bit), word, bit);
405}
406EXPORT_SYMBOL(wake_up_bit);
407
408wait_queue_head_t *bit_waitqueue(void *word, int bit)
409{
410	const int shift = BITS_PER_LONG == 32 ? 5 : 6;
411	const struct zone *zone = page_zone(virt_to_page(word));
412	unsigned long val = (unsigned long)word << shift | bit;
413
414	return &zone->wait_table[hash_long(val, zone->wait_table_bits)];
415}
416EXPORT_SYMBOL(bit_waitqueue);
417
418/*
419 * Manipulate the atomic_t address to produce a better bit waitqueue table hash
420 * index (we're keying off bit -1, but that would produce a horrible hash
421 * value).
422 */
423static inline wait_queue_head_t *atomic_t_waitqueue(atomic_t *p)
424{
425	if (BITS_PER_LONG == 64) {
426		unsigned long q = (unsigned long)p;
427		return bit_waitqueue((void *)(q & ~1), q & 1);
428	}
429	return bit_waitqueue(p, 0);
430}
431
432static int wake_atomic_t_function(wait_queue_t *wait, unsigned mode, int sync,
433				  void *arg)
434{
435	struct wait_bit_key *key = arg;
436	struct wait_bit_queue *wait_bit
437		= container_of(wait, struct wait_bit_queue, wait);
438	atomic_t *val = key->flags;
439
440	if (wait_bit->key.flags != key->flags ||
441	    wait_bit->key.bit_nr != key->bit_nr ||
442	    atomic_read(val) != 0)
443		return 0;
444	return autoremove_wake_function(wait, mode, sync, key);
445}
446
447/*
448 * To allow interruptible waiting and asynchronous (i.e. nonblocking) waiting,
449 * the actions of __wait_on_atomic_t() are permitted return codes.  Nonzero
450 * return codes halt waiting and return.
451 */
452static __sched
453int __wait_on_atomic_t(wait_queue_head_t *wq, struct wait_bit_queue *q,
454		       int (*action)(atomic_t *), unsigned mode)
455{
456	atomic_t *val;
457	int ret = 0;
458
459	do {
460		prepare_to_wait(wq, &q->wait, mode);
461		val = q->key.flags;
462		if (atomic_read(val) == 0)
463			break;
464		ret = (*action)(val);
465	} while (!ret && atomic_read(val) != 0);
466	finish_wait(wq, &q->wait);
467	return ret;
468}
469
470#define DEFINE_WAIT_ATOMIC_T(name, p)					\
471	struct wait_bit_queue name = {					\
472		.key = __WAIT_ATOMIC_T_KEY_INITIALIZER(p),		\
473		.wait	= {						\
474			.private	= current,			\
475			.func		= wake_atomic_t_function,	\
476			.task_list	=				\
477				LIST_HEAD_INIT((name).wait.task_list),	\
478		},							\
479	}
480
481__sched int out_of_line_wait_on_atomic_t(atomic_t *p, int (*action)(atomic_t *),
482					 unsigned mode)
483{
484	wait_queue_head_t *wq = atomic_t_waitqueue(p);
485	DEFINE_WAIT_ATOMIC_T(wait, p);
486
487	return __wait_on_atomic_t(wq, &wait, action, mode);
488}
489EXPORT_SYMBOL(out_of_line_wait_on_atomic_t);
490
491/**
492 * wake_up_atomic_t - Wake up a waiter on a atomic_t
493 * @p: The atomic_t being waited on, a kernel virtual address
494 *
495 * Wake up anyone waiting for the atomic_t to go to zero.
496 *
497 * Abuse the bit-waker function and its waitqueue hash table set (the atomic_t
498 * check is done by the waiter's wake function, not the by the waker itself).
499 */
500void wake_up_atomic_t(atomic_t *p)
501{
502	__wake_up_bit(atomic_t_waitqueue(p), p, WAIT_ATOMIC_T_BIT_NR);
503}
504EXPORT_SYMBOL(wake_up_atomic_t);