projects/linux·blob v2.6.38-rc4 · refs

289 lines · 8.2 KiB

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 noone 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);