wait_bit.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2
  3#include <linux/sched/debug.h>
  4#include "sched.h"
  5
  6/*
  7 * The implementation of the wait_bit*() and related waiting APIs:
  8 */
  9
 10#define WAIT_TABLE_BITS 8
 11#define WAIT_TABLE_SIZE (1 << WAIT_TABLE_BITS)
 12
 13static wait_queue_head_t bit_wait_table[WAIT_TABLE_SIZE] __cacheline_aligned;
 14
 15wait_queue_head_t *bit_waitqueue(unsigned long *word, int bit)
 16{
 17	const int shift = BITS_PER_LONG == 32 ? 5 : 6;
 18	unsigned long val = (unsigned long)word << shift | bit;
 19
 20	return bit_wait_table + hash_long(val, WAIT_TABLE_BITS);
 21}
 22EXPORT_SYMBOL(bit_waitqueue);
 23
 24int wake_bit_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *arg)
 25{
 26	struct wait_bit_key *key = arg;
 27	struct wait_bit_queue_entry *wait_bit = container_of(wq_entry, struct wait_bit_queue_entry, wq_entry);
 28
 29	if (wait_bit->key.flags != key->flags ||
 30			wait_bit->key.bit_nr != key->bit_nr ||
 31			test_bit(key->bit_nr, key->flags))
 32		return 0;
 33
 34	return autoremove_wake_function(wq_entry, mode, sync, key);
 35}
 36EXPORT_SYMBOL(wake_bit_function);
 37
 38/*
 39 * To allow interruptible waiting and asynchronous (i.e. non-blocking)
 40 * waiting, the actions of __wait_on_bit() and __wait_on_bit_lock() are
 41 * permitted return codes. Nonzero return codes halt waiting and return.
 42 */
 43int __sched
 44__wait_on_bit(struct wait_queue_head *wq_head, struct wait_bit_queue_entry *wbq_entry,
 45	      wait_bit_action_f *action, unsigned mode)
 46{
 47	int ret = 0;
 48
 49	do {
 50		prepare_to_wait(wq_head, &wbq_entry->wq_entry, mode);
 51		if (test_bit(wbq_entry->key.bit_nr, wbq_entry->key.flags))
 52			ret = (*action)(&wbq_entry->key, mode);
 53	} while (test_bit_acquire(wbq_entry->key.bit_nr, wbq_entry->key.flags) && !ret);
 54
 55	finish_wait(wq_head, &wbq_entry->wq_entry);
 56
 57	return ret;
 58}
 59EXPORT_SYMBOL(__wait_on_bit);
 60
 61int __sched out_of_line_wait_on_bit(unsigned long *word, int bit,
 62				    wait_bit_action_f *action, unsigned mode)
 63{
 64	struct wait_queue_head *wq_head = bit_waitqueue(word, bit);
 65	DEFINE_WAIT_BIT(wq_entry, word, bit);
 66
 67	return __wait_on_bit(wq_head, &wq_entry, action, mode);
 68}
 69EXPORT_SYMBOL(out_of_line_wait_on_bit);
 70
 71int __sched out_of_line_wait_on_bit_timeout(
 72	unsigned long *word, int bit, wait_bit_action_f *action,
 73	unsigned mode, unsigned long timeout)
 74{
 75	struct wait_queue_head *wq_head = bit_waitqueue(word, bit);
 76	DEFINE_WAIT_BIT(wq_entry, word, bit);
 77
 78	wq_entry.key.timeout = jiffies + timeout;
 79
 80	return __wait_on_bit(wq_head, &wq_entry, action, mode);
 81}
 82EXPORT_SYMBOL_GPL(out_of_line_wait_on_bit_timeout);
 83
 84int __sched
 85__wait_on_bit_lock(struct wait_queue_head *wq_head, struct wait_bit_queue_entry *wbq_entry,
 86			wait_bit_action_f *action, unsigned mode)
 87{
 88	int ret = 0;
 89
 90	for (;;) {
 91		prepare_to_wait_exclusive(wq_head, &wbq_entry->wq_entry, mode);
 92		if (test_bit(wbq_entry->key.bit_nr, wbq_entry->key.flags)) {
 93			ret = action(&wbq_entry->key, mode);
 94			/*
 95			 * See the comment in prepare_to_wait_event().
 96			 * finish_wait() does not necessarily takes wwq_head->lock,
 97			 * but test_and_set_bit() implies mb() which pairs with
 98			 * smp_mb__after_atomic() before wake_up_page().
 99			 */
100			if (ret)
101				finish_wait(wq_head, &wbq_entry->wq_entry);
102		}
103		if (!test_and_set_bit(wbq_entry->key.bit_nr, wbq_entry->key.flags)) {
104			if (!ret)
105				finish_wait(wq_head, &wbq_entry->wq_entry);
106			return 0;
107		} else if (ret) {
108			return ret;
109		}
110	}
111}
112EXPORT_SYMBOL(__wait_on_bit_lock);
113
114int __sched out_of_line_wait_on_bit_lock(unsigned long *word, int bit,
115					 wait_bit_action_f *action, unsigned mode)
116{
117	struct wait_queue_head *wq_head = bit_waitqueue(word, bit);
118	DEFINE_WAIT_BIT(wq_entry, word, bit);
119
120	return __wait_on_bit_lock(wq_head, &wq_entry, action, mode);
121}
122EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);
123
124void __wake_up_bit(struct wait_queue_head *wq_head, unsigned long *word, int bit)
125{
126	struct wait_bit_key key = __WAIT_BIT_KEY_INITIALIZER(word, bit);
127
128	if (waitqueue_active(wq_head))
129		__wake_up(wq_head, TASK_NORMAL, 1, &key);
130}
131EXPORT_SYMBOL(__wake_up_bit);
132
133/**
134 * wake_up_bit - wake up waiters on a bit
135 * @word: the address containing the bit being waited on
136 * @bit: the bit at that address being waited on
137 *
138 * Wake up any process waiting in wait_on_bit() or similar for the
139 * given bit to be cleared.
140 *
141 * The wake-up is sent to tasks in a waitqueue selected by hash from a
142 * shared pool.  Only those tasks on that queue which have requested
143 * wake_up on this specific address and bit will be woken, and only if the
144 * bit is clear.
145 *
146 * In order for this to function properly there must be a full memory
147 * barrier after the bit is cleared and before this function is called.
148 * If the bit was cleared atomically, such as a by clear_bit() then
149 * smb_mb__after_atomic() can be used, othwewise smb_mb() is needed.
150 * If the bit was cleared with a fully-ordered operation, no further
151 * barrier is required.
152 *
153 * Normally the bit should be cleared by an operation with RELEASE
154 * semantics so that any changes to memory made before the bit is
155 * cleared are guaranteed to be visible after the matching wait_on_bit()
156 * completes.
157 */
158void wake_up_bit(unsigned long *word, int bit)
159{
160	__wake_up_bit(bit_waitqueue(word, bit), word, bit);
161}
162EXPORT_SYMBOL(wake_up_bit);
163
164wait_queue_head_t *__var_waitqueue(void *p)
165{
166	return bit_wait_table + hash_ptr(p, WAIT_TABLE_BITS);
167}
168EXPORT_SYMBOL(__var_waitqueue);
169
170static int
171var_wake_function(struct wait_queue_entry *wq_entry, unsigned int mode,
172		  int sync, void *arg)
173{
174	struct wait_bit_key *key = arg;
175	struct wait_bit_queue_entry *wbq_entry =
176		container_of(wq_entry, struct wait_bit_queue_entry, wq_entry);
177
178	if (wbq_entry->key.flags != key->flags ||
179	    wbq_entry->key.bit_nr != key->bit_nr)
180		return 0;
181
182	return autoremove_wake_function(wq_entry, mode, sync, key);
183}
184
185void init_wait_var_entry(struct wait_bit_queue_entry *wbq_entry, void *var, int flags)
186{
187	*wbq_entry = (struct wait_bit_queue_entry){
188		.key = {
189			.flags	= (var),
190			.bit_nr = -1,
191		},
192		.wq_entry = {
193			.flags	 = flags,
194			.private = current,
195			.func	 = var_wake_function,
196			.entry	 = LIST_HEAD_INIT(wbq_entry->wq_entry.entry),
197		},
198	};
199}
200EXPORT_SYMBOL(init_wait_var_entry);
201
202/**
203 * wake_up_var - wake up waiters on a variable (kernel address)
204 * @var: the address of the variable being waited on
205 *
206 * Wake up any process waiting in wait_var_event() or similar for the
207 * given variable to change.  wait_var_event() can be waiting for an
208 * arbitrary condition to be true and associates that condition with an
209 * address.  Calling wake_up_var() suggests that the condition has been
210 * made true, but does not strictly require the condtion to use the
211 * address given.
212 *
213 * The wake-up is sent to tasks in a waitqueue selected by hash from a
214 * shared pool.  Only those tasks on that queue which have requested
215 * wake_up on this specific address will be woken.
216 *
217 * In order for this to function properly there must be a full memory
218 * barrier after the variable is updated (or more accurately, after the
219 * condition waited on has been made to be true) and before this function
220 * is called.  If the variable was updated atomically, such as a by
221 * atomic_dec() then smb_mb__after_atomic() can be used.  If the
222 * variable was updated by a fully ordered operation such as
223 * atomic_dec_and_test() then no extra barrier is required.  Otherwise
224 * smb_mb() is needed.
225 *
226 * Normally the variable should be updated (the condition should be made
227 * to be true) by an operation with RELEASE semantics such as
228 * smp_store_release() so that any changes to memory made before the
229 * variable was updated are guaranteed to be visible after the matching
230 * wait_var_event() completes.
231 */
232void wake_up_var(void *var)
233{
234	__wake_up_bit(__var_waitqueue(var), var, -1);
235}
236EXPORT_SYMBOL(wake_up_var);
237
238__sched int bit_wait(struct wait_bit_key *word, int mode)
239{
240	schedule();
241	if (signal_pending_state(mode, current))
242		return -EINTR;
243
244	return 0;
245}
246EXPORT_SYMBOL(bit_wait);
247
248__sched int bit_wait_io(struct wait_bit_key *word, int mode)
249{
250	io_schedule();
251	if (signal_pending_state(mode, current))
252		return -EINTR;
253
254	return 0;
255}
256EXPORT_SYMBOL(bit_wait_io);
257
258__sched int bit_wait_timeout(struct wait_bit_key *word, int mode)
259{
260	unsigned long now = READ_ONCE(jiffies);
261
262	if (time_after_eq(now, word->timeout))
263		return -EAGAIN;
264	schedule_timeout(word->timeout - now);
265	if (signal_pending_state(mode, current))
266		return -EINTR;
267
268	return 0;
269}
270EXPORT_SYMBOL_GPL(bit_wait_timeout);
271
272void __init wait_bit_init(void)
273{
274	int i;
275
276	for (i = 0; i < WAIT_TABLE_SIZE; i++)
277		init_waitqueue_head(bit_wait_table + i);
278}