1/*
  2 * Generic waiting primitives.
  3 *
  4 * (C) 2004 William Irwin, Oracle
  5 */
  6#include <linux/init.h>
  7#include <linux/module.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, struct lock_class_key *key)
 14{
 15	spin_lock_init(&q->lock);
 16	lockdep_set_class(&q->lock, key);
 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 * Note: we use "set_current_state()" _after_ the wait-queue add,
 57 * because we need a memory barrier there on SMP, so that any
 58 * wake-function that tests for the wait-queue being active
 59 * will be guaranteed to see waitqueue addition _or_ subsequent
 60 * tests in this thread will see the wakeup having taken place.
 61 *
 62 * The spin_unlock() itself is semi-permeable and only protects
 63 * one way (it only protects stuff inside the critical region and
 64 * stops them from bleeding out - it would still allow subsequent
 65 * loads to move into the critical region).
 66 */
 67void
 68prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, int state)
 69{
 70	unsigned long flags;
 71
 72	wait->flags &= ~WQ_FLAG_EXCLUSIVE;
 73	spin_lock_irqsave(&q->lock, flags);
 74	if (list_empty(&wait->task_list))
 75		__add_wait_queue(q, wait);
 76	set_current_state(state);
 77	spin_unlock_irqrestore(&q->lock, flags);
 78}
 79EXPORT_SYMBOL(prepare_to_wait);
 80
 81void
 82prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state)
 83{
 84	unsigned long flags;
 85
 86	wait->flags |= WQ_FLAG_EXCLUSIVE;
 87	spin_lock_irqsave(&q->lock, flags);
 88	if (list_empty(&wait->task_list))
 89		__add_wait_queue_tail(q, wait);
 90	set_current_state(state);
 91	spin_unlock_irqrestore(&q->lock, flags);
 92}
 93EXPORT_SYMBOL(prepare_to_wait_exclusive);
 94
 95/**
 96 * finish_wait - clean up after waiting in a queue
 97 * @q: waitqueue waited on
 98 * @wait: wait descriptor
 99 *
100 * Sets current thread back to running state and removes
101 * the wait descriptor from the given waitqueue if still
102 * queued.
103 */
104void finish_wait(wait_queue_head_t *q, wait_queue_t *wait)
105{
106	unsigned long flags;
107
108	__set_current_state(TASK_RUNNING);
109	/*
110	 * We can check for list emptiness outside the lock
111	 * IFF:
112	 *  - we use the "careful" check that verifies both
113	 *    the next and prev pointers, so that there cannot
114	 *    be any half-pending updates in progress on other
115	 *    CPU's that we haven't seen yet (and that might
116	 *    still change the stack area.
117	 * and
118	 *  - all other users take the lock (ie we can only
119	 *    have _one_ other CPU that looks at or modifies
120	 *    the list).
121	 */
122	if (!list_empty_careful(&wait->task_list)) {
123		spin_lock_irqsave(&q->lock, flags);
124		list_del_init(&wait->task_list);
125		spin_unlock_irqrestore(&q->lock, flags);
126	}
127}
128EXPORT_SYMBOL(finish_wait);
129
130/**
131 * abort_exclusive_wait - abort exclusive waiting in a queue
132 * @q: waitqueue waited on
133 * @wait: wait descriptor
134 * @mode: runstate of the waiter to be woken
135 * @key: key to identify a wait bit queue or %NULL
136 *
137 * Sets current thread back to running state and removes
138 * the wait descriptor from the given waitqueue if still
139 * queued.
140 *
141 * Wakes up the next waiter if the caller is concurrently
142 * woken up through the queue.
143 *
144 * This prevents waiter starvation where an exclusive waiter
145 * aborts and is woken up concurrently and no one wakes up
146 * the next waiter.
147 */
148void abort_exclusive_wait(wait_queue_head_t *q, wait_queue_t *wait,
149			unsigned int mode, void *key)
150{
151	unsigned long flags;
152
153	__set_current_state(TASK_RUNNING);
154	spin_lock_irqsave(&q->lock, flags);
155	if (!list_empty(&wait->task_list))
156		list_del_init(&wait->task_list);
157	else if (waitqueue_active(q))
158		__wake_up_locked_key(q, mode, key);
159	spin_unlock_irqrestore(&q->lock, flags);
160}
161EXPORT_SYMBOL(abort_exclusive_wait);
162
163int autoremove_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
164{
165	int ret = default_wake_function(wait, mode, sync, key);
166
167	if (ret)
168		list_del_init(&wait->task_list);
169	return ret;
170}
171EXPORT_SYMBOL(autoremove_wake_function);
172
173int wake_bit_function(wait_queue_t *wait, unsigned mode, int sync, void *arg)
174{
175	struct wait_bit_key *key = arg;
176	struct wait_bit_queue *wait_bit
177		= container_of(wait, struct wait_bit_queue, wait);
178
179	if (wait_bit->key.flags != key->flags ||
180			wait_bit->key.bit_nr != key->bit_nr ||
181			test_bit(key->bit_nr, key->flags))
182		return 0;
183	else
184		return autoremove_wake_function(wait, mode, sync, key);
185}
186EXPORT_SYMBOL(wake_bit_function);
187
188/*
189 * To allow interruptible waiting and asynchronous (i.e. nonblocking)
190 * waiting, the actions of __wait_on_bit() and __wait_on_bit_lock() are
191 * permitted return codes. Nonzero return codes halt waiting and return.
192 */
193int __sched
194__wait_on_bit(wait_queue_head_t *wq, struct wait_bit_queue *q,
195			int (*action)(void *), unsigned mode)
196{
197	int ret = 0;
198
199	do {
200		prepare_to_wait(wq, &q->wait, mode);
201		if (test_bit(q->key.bit_nr, q->key.flags))
202			ret = (*action)(q->key.flags);
203	} while (test_bit(q->key.bit_nr, q->key.flags) && !ret);
204	finish_wait(wq, &q->wait);
205	return ret;
206}
207EXPORT_SYMBOL(__wait_on_bit);
208
209int __sched out_of_line_wait_on_bit(void *word, int bit,
210					int (*action)(void *), unsigned mode)
211{
212	wait_queue_head_t *wq = bit_waitqueue(word, bit);
213	DEFINE_WAIT_BIT(wait, word, bit);
214
215	return __wait_on_bit(wq, &wait, action, mode);
216}
217EXPORT_SYMBOL(out_of_line_wait_on_bit);
218
219int __sched
220__wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
221			int (*action)(void *), unsigned mode)
222{
223	do {
224		int ret;
225
226		prepare_to_wait_exclusive(wq, &q->wait, mode);
227		if (!test_bit(q->key.bit_nr, q->key.flags))
228			continue;
229		ret = action(q->key.flags);
230		if (!ret)
231			continue;
232		abort_exclusive_wait(wq, &q->wait, mode, &q->key);
233		return ret;
234	} while (test_and_set_bit(q->key.bit_nr, q->key.flags));
235	finish_wait(wq, &q->wait);
236	return 0;
237}
238EXPORT_SYMBOL(__wait_on_bit_lock);
239
240int __sched out_of_line_wait_on_bit_lock(void *word, int bit,
241					int (*action)(void *), unsigned mode)
242{
243	wait_queue_head_t *wq = bit_waitqueue(word, bit);
244	DEFINE_WAIT_BIT(wait, word, bit);
245
246	return __wait_on_bit_lock(wq, &wait, action, mode);
247}
248EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);
249
250void __wake_up_bit(wait_queue_head_t *wq, void *word, int bit)
251{
252	struct wait_bit_key key = __WAIT_BIT_KEY_INITIALIZER(word, bit);
253	if (waitqueue_active(wq))
254		__wake_up(wq, TASK_NORMAL, 1, &key);
255}
256EXPORT_SYMBOL(__wake_up_bit);
257
258/**
259 * wake_up_bit - wake up a waiter on a bit
260 * @word: the word being waited on, a kernel virtual address
261 * @bit: the bit of the word being waited on
262 *
263 * There is a standard hashed waitqueue table for generic use. This
264 * is the part of the hashtable's accessor API that wakes up waiters
265 * on a bit. For instance, if one were to have waiters on a bitflag,
266 * one would call wake_up_bit() after clearing the bit.
267 *
268 * In order for this to function properly, as it uses waitqueue_active()
269 * internally, some kind of memory barrier must be done prior to calling
270 * this. Typically, this will be smp_mb__after_clear_bit(), but in some
271 * cases where bitflags are manipulated non-atomically under a lock, one
272 * may need to use a less regular barrier, such fs/inode.c's smp_mb(),
273 * because spin_unlock() does not guarantee a memory barrier.
274 */
275void wake_up_bit(void *word, int bit)
276{
277	__wake_up_bit(bit_waitqueue(word, bit), word, bit);
278}
279EXPORT_SYMBOL(wake_up_bit);
280
281wait_queue_head_t *bit_waitqueue(void *word, int bit)
282{
283	const int shift = BITS_PER_LONG == 32 ? 5 : 6;
284	const struct zone *zone = page_zone(virt_to_page(word));
285	unsigned long val = (unsigned long)word << shift | bit;
286
287	return &zone->wait_table[hash_long(val, zone->wait_table_bits)];
288}
289EXPORT_SYMBOL(bit_waitqueue);