Root/kernel/wait.c

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);
290

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