summaryrefslogtreecommitdiffstats
path: root/kernel/sched/wait_bit.c
blob: c67c6d24adc2a1e38a86e48b20373354c2e1f317 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
/*
 * The implementation of the wait_bit*() and related waiting APIs:
 */
#include "sched.h"

#define WAIT_TABLE_BITS 8
#define WAIT_TABLE_SIZE (1 << WAIT_TABLE_BITS)

static wait_queue_head_t bit_wait_table[WAIT_TABLE_SIZE] __cacheline_aligned;

wait_queue_head_t *bit_waitqueue(void *word, int bit)
{
	const int shift = BITS_PER_LONG == 32 ? 5 : 6;
	unsigned long val = (unsigned long)word << shift | bit;

	return bit_wait_table + hash_long(val, WAIT_TABLE_BITS);
}
EXPORT_SYMBOL(bit_waitqueue);

int wake_bit_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *arg)
{
	struct wait_bit_key *key = arg;
	struct wait_bit_queue_entry *wait_bit = container_of(wq_entry, struct wait_bit_queue_entry, wq_entry);

	if (wait_bit->key.flags != key->flags ||
			wait_bit->key.bit_nr != key->bit_nr ||
			test_bit(key->bit_nr, key->flags))
		return 0;

	return autoremove_wake_function(wq_entry, mode, sync, key);
}
EXPORT_SYMBOL(wake_bit_function);

/*
 * To allow interruptible waiting and asynchronous (i.e. nonblocking)
 * waiting, the actions of __wait_on_bit() and __wait_on_bit_lock() are
 * permitted return codes. Nonzero return codes halt waiting and return.
 */
int __sched
__wait_on_bit(struct wait_queue_head *wq_head, struct wait_bit_queue_entry *wbq_entry,
	      wait_bit_action_f *action, unsigned mode)
{
	int ret = 0;

	do {
		prepare_to_wait(wq_head, &wbq_entry->wq_entry, mode);
		if (test_bit(wbq_entry->key.bit_nr, wbq_entry->key.flags))
			ret = (*action)(&wbq_entry->key, mode);
	} while (test_bit(wbq_entry->key.bit_nr, wbq_entry->key.flags) && !ret);

	finish_wait(wq_head, &wbq_entry->wq_entry);

	return ret;
}
EXPORT_SYMBOL(__wait_on_bit);

int __sched out_of_line_wait_on_bit(void *word, int bit,
				    wait_bit_action_f *action, unsigned mode)
{
	struct wait_queue_head *wq_head = bit_waitqueue(word, bit);
	DEFINE_WAIT_BIT(wq_entry, word, bit);

	return __wait_on_bit(wq_head, &wq_entry, action, mode);
}
EXPORT_SYMBOL(out_of_line_wait_on_bit);

int __sched out_of_line_wait_on_bit_timeout(
	void *word, int bit, wait_bit_action_f *action,
	unsigned mode, unsigned long timeout)
{
	struct wait_queue_head *wq_head = bit_waitqueue(word, bit);
	DEFINE_WAIT_BIT(wq_entry, word, bit);

	wq_entry.key.timeout = jiffies + timeout;

	return __wait_on_bit(wq_head, &wq_entry, action, mode);
}
EXPORT_SYMBOL_GPL(out_of_line_wait_on_bit_timeout);

int __sched
__wait_on_bit_lock(struct wait_queue_head *wq_head, struct wait_bit_queue_entry *wbq_entry,
			wait_bit_action_f *action, unsigned mode)
{
	int ret = 0;

	for (;;) {
		prepare_to_wait_exclusive(wq_head, &wbq_entry->wq_entry, mode);
		if (test_bit(wbq_entry->key.bit_nr, wbq_entry->key.flags)) {
			ret = action(&wbq_entry->key, mode);
			/*
			 * See the comment in prepare_to_wait_event().
			 * finish_wait() does not necessarily takes wwq_head->lock,
			 * but test_and_set_bit() implies mb() which pairs with
			 * smp_mb__after_atomic() before wake_up_page().
			 */
			if (ret)
				finish_wait(wq_head, &wbq_entry->wq_entry);
		}
		if (!test_and_set_bit(wbq_entry->key.bit_nr, wbq_entry->key.flags)) {
			if (!ret)
				finish_wait(wq_head, &wbq_entry->wq_entry);
			return 0;
		} else if (ret) {
			return ret;
		}
	}
}
EXPORT_SYMBOL(__wait_on_bit_lock);

int __sched out_of_line_wait_on_bit_lock(void *word, int bit,
					 wait_bit_action_f *action, unsigned mode)
{
	struct wait_queue_head *wq_head = bit_waitqueue(word, bit);
	DEFINE_WAIT_BIT(wq_entry, word, bit);

	return __wait_on_bit_lock(wq_head, &wq_entry, action, mode);
}
EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);

void __wake_up_bit(struct wait_queue_head *wq_head, void *word, int bit)
{
	struct wait_bit_key key = __WAIT_BIT_KEY_INITIALIZER(word, bit);

	if (waitqueue_active(wq_head))
		__wake_up(wq_head, TASK_NORMAL, 1, &key);
}
EXPORT_SYMBOL(__wake_up_bit);

/**
 * wake_up_bit - wake up a waiter on a bit
 * @word: the word being waited on, a kernel virtual address
 * @bit: the bit of the word being waited on
 *
 * There is a standard hashed waitqueue table for generic use. This
 * is the part of the hashtable's accessor API that wakes up waiters
 * on a bit. For instance, if one were to have waiters on a bitflag,
 * one would call wake_up_bit() after clearing the bit.
 *
 * In order for this to function properly, as it uses waitqueue_active()
 * internally, some kind of memory barrier must be done prior to calling
 * this. Typically, this will be smp_mb__after_atomic(), but in some
 * cases where bitflags are manipulated non-atomically under a lock, one
 * may need to use a less regular barrier, such fs/inode.c's smp_mb(),
 * because spin_unlock() does not guarantee a memory barrier.
 */
void wake_up_bit(void *word, int bit)
{
	__wake_up_bit(bit_waitqueue(word, bit), word, bit);
}
EXPORT_SYMBOL(wake_up_bit);

wait_queue_head_t *__var_waitqueue(void *p)
{
	return bit_wait_table + hash_ptr(p, WAIT_TABLE_BITS);
}
EXPORT_SYMBOL(__var_waitqueue);

static int
var_wake_function(struct wait_queue_entry *wq_entry, unsigned int mode,
		  int sync, void *arg)
{
	struct wait_bit_key *key = arg;
	struct wait_bit_queue_entry *wbq_entry =
		container_of(wq_entry, struct wait_bit_queue_entry, wq_entry);

	if (wbq_entry->key.flags != key->flags ||
	    wbq_entry->key.bit_nr != key->bit_nr)
		return 0;

	return autoremove_wake_function(wq_entry, mode, sync, key);
}

void init_wait_var_entry(struct wait_bit_queue_entry *wbq_entry, void *var, int flags)
{
	*wbq_entry = (struct wait_bit_queue_entry){
		.key = {
			.flags	= (var),
			.bit_nr = -1,
		},
		.wq_entry = {
			.private = current,
			.func	 = var_wake_function,
			.entry	 = LIST_HEAD_INIT(wbq_entry->wq_entry.entry),
		},
	};
}
EXPORT_SYMBOL(init_wait_var_entry);

void wake_up_var(void *var)
{
	__wake_up_bit(__var_waitqueue(var), var, -1);
}
EXPORT_SYMBOL(wake_up_var);

__sched int bit_wait(struct wait_bit_key *word, int mode)
{
	schedule();
	if (signal_pending_state(mode, current))
		return -EINTR;

	return 0;
}
EXPORT_SYMBOL(bit_wait);

__sched int bit_wait_io(struct wait_bit_key *word, int mode)
{
	io_schedule();
	if (signal_pending_state(mode, current))
		return -EINTR;

	return 0;
}
EXPORT_SYMBOL(bit_wait_io);

__sched int bit_wait_timeout(struct wait_bit_key *word, int mode)
{
	unsigned long now = READ_ONCE(jiffies);

	if (time_after_eq(now, word->timeout))
		return -EAGAIN;
	schedule_timeout(word->timeout - now);
	if (signal_pending_state(mode, current))
		return -EINTR;

	return 0;
}
EXPORT_SYMBOL_GPL(bit_wait_timeout);

__sched int bit_wait_io_timeout(struct wait_bit_key *word, int mode)
{
	unsigned long now = READ_ONCE(jiffies);

	if (time_after_eq(now, word->timeout))
		return -EAGAIN;
	io_schedule_timeout(word->timeout - now);
	if (signal_pending_state(mode, current))
		return -EINTR;

	return 0;
}
EXPORT_SYMBOL_GPL(bit_wait_io_timeout);

void __init wait_bit_init(void)
{
	int i;

	for (i = 0; i < WAIT_TABLE_SIZE; i++)
		init_waitqueue_head(bit_wait_table + i);
}