1// SPDX-License-Identifier: GPL-2.0-only
2
3/*
4 * The implementation of the wait_bit*() and related waiting APIs:
5 */
6
7#define WAIT_TABLE_BITS 8
8#define WAIT_TABLE_SIZE (1 << WAIT_TABLE_BITS)
9
10static wait_queue_head_t bit_wait_table[WAIT_TABLE_SIZE] __cacheline_aligned;
11
12wait_queue_head_t *bit_waitqueue(void *word, int bit)
13{
14	const int shift = BITS_PER_LONG == 32 ? 5 : 6;
15	unsigned long val = (unsigned long)word << shift | bit;
16
17	return bit_wait_table + hash_long(val, WAIT_TABLE_BITS);
18}
19EXPORT_SYMBOL(bit_waitqueue);
20
21int wake_bit_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *arg)
22{
23	struct wait_bit_key *key = arg;
24	struct wait_bit_queue_entry *wait_bit = container_of(wq_entry, struct wait_bit_queue_entry, wq_entry);
25
26	if (wait_bit->key.flags != key->flags ||
27			wait_bit->key.bit_nr != key->bit_nr ||
28			test_bit(key->bit_nr, key->flags))
29		return 0;
30
31	return autoremove_wake_function(wq_entry, mode, sync, key);
32}
33EXPORT_SYMBOL(wake_bit_function);
34
35/*
36 * To allow interruptible waiting and asynchronous (i.e. nonblocking)
37 * waiting, the actions of __wait_on_bit() and __wait_on_bit_lock() are
38 * permitted return codes. Nonzero return codes halt waiting and return.
39 */
40int __sched
41__wait_on_bit(struct wait_queue_head *wq_head, struct wait_bit_queue_entry *wbq_entry,
42	      wait_bit_action_f *action, unsigned mode)
43{
44	int ret = 0;
45
46	do {
47		prepare_to_wait(wq_head, &wbq_entry->wq_entry, mode);
48		if (test_bit(wbq_entry->key.bit_nr, wbq_entry->key.flags))
49			ret = (*action)(&wbq_entry->key, mode);
50	} while (test_bit_acquire(wbq_entry->key.bit_nr, wbq_entry->key.flags) && !ret);
51
52	finish_wait(wq_head, &wbq_entry->wq_entry);
53
54	return ret;
55}
56EXPORT_SYMBOL(__wait_on_bit);
57
58int __sched out_of_line_wait_on_bit(void *word, int bit,
59				    wait_bit_action_f *action, unsigned mode)
60{
61	struct wait_queue_head *wq_head = bit_waitqueue(word, bit);
62	DEFINE_WAIT_BIT(wq_entry, word, bit);
63
64	return __wait_on_bit(wq_head, &wq_entry, action, mode);
65}
66EXPORT_SYMBOL(out_of_line_wait_on_bit);
67
68int __sched out_of_line_wait_on_bit_timeout(
69	void *word, int bit, wait_bit_action_f *action,
70	unsigned mode, unsigned long timeout)
71{
72	struct wait_queue_head *wq_head = bit_waitqueue(word, bit);
73	DEFINE_WAIT_BIT(wq_entry, word, bit);
74
75	wq_entry.key.timeout = jiffies + timeout;
76
77	return __wait_on_bit(wq_head, &wq_entry, action, mode);
78}
79EXPORT_SYMBOL_GPL(out_of_line_wait_on_bit_timeout);
80
81int __sched
82__wait_on_bit_lock(struct wait_queue_head *wq_head, struct wait_bit_queue_entry *wbq_entry,
83			wait_bit_action_f *action, unsigned mode)
84{
85	int ret = 0;
86
87	for (;;) {
88		prepare_to_wait_exclusive(wq_head, &wbq_entry->wq_entry, mode);
89		if (test_bit(wbq_entry->key.bit_nr, wbq_entry->key.flags)) {
90			ret = action(&wbq_entry->key, mode);
91			/*
92			 * See the comment in prepare_to_wait_event().
93			 * finish_wait() does not necessarily takes wwq_head->lock,
94			 * but test_and_set_bit() implies mb() which pairs with
95			 * smp_mb__after_atomic() before wake_up_page().
96			 */
97			if (ret)
98				finish_wait(wq_head, &wbq_entry->wq_entry);
99		}
100		if (!test_and_set_bit(wbq_entry->key.bit_nr, wbq_entry->key.flags)) {
101			if (!ret)
102				finish_wait(wq_head, &wbq_entry->wq_entry);
103			return 0;
104		} else if (ret) {
105			return ret;
106		}
107	}
108}
109EXPORT_SYMBOL(__wait_on_bit_lock);
110
111int __sched out_of_line_wait_on_bit_lock(void *word, int bit,
112					 wait_bit_action_f *action, unsigned mode)
113{
114	struct wait_queue_head *wq_head = bit_waitqueue(word, bit);
115	DEFINE_WAIT_BIT(wq_entry, word, bit);
116
117	return __wait_on_bit_lock(wq_head, &wq_entry, action, mode);
118}
119EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);
120
121void __wake_up_bit(struct wait_queue_head *wq_head, void *word, int bit)
122{
123	struct wait_bit_key key = __WAIT_BIT_KEY_INITIALIZER(word, bit);
124
125	if (waitqueue_active(wq_head))
126		__wake_up(wq_head, TASK_NORMAL, 1, &key);
127}
128EXPORT_SYMBOL(__wake_up_bit);
129
130/**
131 * wake_up_bit - wake up a waiter on a bit
132 * @word: the word being waited on, a kernel virtual address
133 * @bit: the bit of the word being waited on
134 *
135 * There is a standard hashed waitqueue table for generic use. This
136 * is the part of the hashtable's accessor API that wakes up waiters
137 * on a bit. For instance, if one were to have waiters on a bitflag,
138 * one would call wake_up_bit() after clearing the bit.
139 *
140 * In order for this to function properly, as it uses waitqueue_active()
141 * internally, some kind of memory barrier must be done prior to calling
142 * this. Typically, this will be smp_mb__after_atomic(), but in some
143 * cases where bitflags are manipulated non-atomically under a lock, one
144 * may need to use a less regular barrier, such fs/inode.c's smp_mb(),
145 * because spin_unlock() does not guarantee a memory barrier.
146 */
147void wake_up_bit(void *word, int bit)
148{
149	__wake_up_bit(bit_waitqueue(word, bit), word, bit);
150}
151EXPORT_SYMBOL(wake_up_bit);
152
153wait_queue_head_t *__var_waitqueue(void *p)
154{
155	return bit_wait_table + hash_ptr(p, WAIT_TABLE_BITS);
156}
157EXPORT_SYMBOL(__var_waitqueue);
158
159static int
160var_wake_function(struct wait_queue_entry *wq_entry, unsigned int mode,
161		  int sync, void *arg)
162{
163	struct wait_bit_key *key = arg;
164	struct wait_bit_queue_entry *wbq_entry =
165		container_of(wq_entry, struct wait_bit_queue_entry, wq_entry);
166
167	if (wbq_entry->key.flags != key->flags ||
168	    wbq_entry->key.bit_nr != key->bit_nr)
169		return 0;
170
171	return autoremove_wake_function(wq_entry, mode, sync, key);
172}
173
174void init_wait_var_entry(struct wait_bit_queue_entry *wbq_entry, void *var, int flags)
175{
176	*wbq_entry = (struct wait_bit_queue_entry){
177		.key = {
178			.flags	= (var),
179			.bit_nr = -1,
180		},
181		.wq_entry = {
182			.flags	 = flags,
183			.private = current,
184			.func	 = var_wake_function,
185			.entry	 = LIST_HEAD_INIT(wbq_entry->wq_entry.entry),
186		},
187	};
188}
189EXPORT_SYMBOL(init_wait_var_entry);
190
191void wake_up_var(void *var)
192{
193	__wake_up_bit(__var_waitqueue(var), var, -1);
194}
195EXPORT_SYMBOL(wake_up_var);
196
197__sched int bit_wait(struct wait_bit_key *word, int mode)
198{
199	schedule();
200	if (signal_pending_state(mode, current))
201		return -EINTR;
202
203	return 0;
204}
205EXPORT_SYMBOL(bit_wait);
206
207__sched int bit_wait_io(struct wait_bit_key *word, int mode)
208{
209	io_schedule();
210	if (signal_pending_state(mode, current))
211		return -EINTR;
212
213	return 0;
214}
215EXPORT_SYMBOL(bit_wait_io);
216
217__sched int bit_wait_timeout(struct wait_bit_key *word, int mode)
218{
219	unsigned long now = READ_ONCE(jiffies);
220
221	if (time_after_eq(now, word->timeout))
222		return -EAGAIN;
223	schedule_timeout(word->timeout - now);
224	if (signal_pending_state(mode, current))
225		return -EINTR;
226
227	return 0;
228}
229EXPORT_SYMBOL_GPL(bit_wait_timeout);
230
231__sched int bit_wait_io_timeout(struct wait_bit_key *word, int mode)
232{
233	unsigned long now = READ_ONCE(jiffies);
234
235	if (time_after_eq(now, word->timeout))
236		return -EAGAIN;
237	io_schedule_timeout(word->timeout - now);
238	if (signal_pending_state(mode, current))
239		return -EINTR;
240
241	return 0;
242}
243EXPORT_SYMBOL_GPL(bit_wait_io_timeout);
244
245void __init wait_bit_init(void)
246{
247	int i;
248
249	for (i = 0; i < WAIT_TABLE_SIZE; i++)
250		init_waitqueue_head(bit_wait_table + i);
251}
252