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(unsigned long *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. non-blocking)
 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(unsigned long *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	unsigned long *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(unsigned long *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, unsigned long *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 waiters on a bit
132 * @word: the address containing the bit being waited on
133 * @bit: the bit at that address being waited on
134 *
135 * Wake up any process waiting in wait_on_bit() or similar for the
136 * given bit to be cleared.
137 *
138 * The wake-up is sent to tasks in a waitqueue selected by hash from a
139 * shared pool.  Only those tasks on that queue which have requested
140 * wake_up on this specific address and bit will be woken, and only if the
141 * bit is clear.
142 *
143 * In order for this to function properly there must be a full memory
144 * barrier after the bit is cleared and before this function is called.
145 * If the bit was cleared atomically, such as a by clear_bit() then
146 * smb_mb__after_atomic() can be used, othwewise smb_mb() is needed.
147 * If the bit was cleared with a fully-ordered operation, no further
148 * barrier is required.
149 *
150 * Normally the bit should be cleared by an operation with RELEASE
151 * semantics so that any changes to memory made before the bit is
152 * cleared are guaranteed to be visible after the matching wait_on_bit()
153 * completes.
154 */
155void wake_up_bit(unsigned long *word, int bit)
156{
157	__wake_up_bit(bit_waitqueue(word, bit), word, bit);
158}
159EXPORT_SYMBOL(wake_up_bit);
160
161wait_queue_head_t *__var_waitqueue(void *p)
162{
163	return bit_wait_table + hash_ptr(p, WAIT_TABLE_BITS);
164}
165EXPORT_SYMBOL(__var_waitqueue);
166
167static int
168var_wake_function(struct wait_queue_entry *wq_entry, unsigned int mode,
169		  int sync, void *arg)
170{
171	struct wait_bit_key *key = arg;
172	struct wait_bit_queue_entry *wbq_entry =
173		container_of(wq_entry, struct wait_bit_queue_entry, wq_entry);
174
175	if (wbq_entry->key.flags != key->flags ||
176	    wbq_entry->key.bit_nr != key->bit_nr)
177		return 0;
178
179	return autoremove_wake_function(wq_entry, mode, sync, key);
180}
181
182void init_wait_var_entry(struct wait_bit_queue_entry *wbq_entry, void *var, int flags)
183{
184	*wbq_entry = (struct wait_bit_queue_entry){
185		.key = {
186			.flags	= (var),
187			.bit_nr = -1,
188		},
189		.wq_entry = {
190			.flags	 = flags,
191			.private = current,
192			.func	 = var_wake_function,
193			.entry	 = LIST_HEAD_INIT(wbq_entry->wq_entry.entry),
194		},
195	};
196}
197EXPORT_SYMBOL(init_wait_var_entry);
198
199/**
200 * wake_up_var - wake up waiters on a variable (kernel address)
201 * @var: the address of the variable being waited on
202 *
203 * Wake up any process waiting in wait_var_event() or similar for the
204 * given variable to change.  wait_var_event() can be waiting for an
205 * arbitrary condition to be true and associates that condition with an
206 * address.  Calling wake_up_var() suggests that the condition has been
207 * made true, but does not strictly require the condtion to use the
208 * address given.
209 *
210 * The wake-up is sent to tasks in a waitqueue selected by hash from a
211 * shared pool.  Only those tasks on that queue which have requested
212 * wake_up on this specific address will be woken.
213 *
214 * In order for this to function properly there must be a full memory
215 * barrier after the variable is updated (or more accurately, after the
216 * condition waited on has been made to be true) and before this function
217 * is called.  If the variable was updated atomically, such as a by
218 * atomic_dec() then smb_mb__after_atomic() can be used.  If the
219 * variable was updated by a fully ordered operation such as
220 * atomic_dec_and_test() then no extra barrier is required.  Otherwise
221 * smb_mb() is needed.
222 *
223 * Normally the variable should be updated (the condition should be made
224 * to be true) by an operation with RELEASE semantics such as
225 * smp_store_release() so that any changes to memory made before the
226 * variable was updated are guaranteed to be visible after the matching
227 * wait_var_event() completes.
228 */
229void wake_up_var(void *var)
230{
231	__wake_up_bit(__var_waitqueue(var), var, -1);
232}
233EXPORT_SYMBOL(wake_up_var);
234
235__sched int bit_wait(struct wait_bit_key *word, int mode)
236{
237	schedule();
238	if (signal_pending_state(mode, current))
239		return -EINTR;
240
241	return 0;
242}
243EXPORT_SYMBOL(bit_wait);
244
245__sched int bit_wait_io(struct wait_bit_key *word, int mode)
246{
247	io_schedule();
248	if (signal_pending_state(mode, current))
249		return -EINTR;
250
251	return 0;
252}
253EXPORT_SYMBOL(bit_wait_io);
254
255__sched int bit_wait_timeout(struct wait_bit_key *word, int mode)
256{
257	unsigned long now = READ_ONCE(jiffies);
258
259	if (time_after_eq(now, word->timeout))
260		return -EAGAIN;
261	schedule_timeout(word->timeout - now);
262	if (signal_pending_state(mode, current))
263		return -EINTR;
264
265	return 0;
266}
267EXPORT_SYMBOL_GPL(bit_wait_timeout);
268
269void __init wait_bit_init(void)
270{
271	int i;
272
273	for (i = 0; i < WAIT_TABLE_SIZE; i++)
274		init_waitqueue_head(bit_wait_table + i);
275}