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