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 
10 static wait_queue_head_t bit_wait_table[WAIT_TABLE_SIZE] __cacheline_aligned;
11 
bit_waitqueue(void * word,int bit)12 wait_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 }
19 EXPORT_SYMBOL(bit_waitqueue);
20 
wake_bit_function(struct wait_queue_entry * wq_entry,unsigned mode,int sync,void * arg)21 int 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 }
33 EXPORT_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  */
40 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)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 }
56 EXPORT_SYMBOL(__wait_on_bit);
57 
out_of_line_wait_on_bit(void * word,int bit,wait_bit_action_f * action,unsigned mode)58 int __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 }
66 EXPORT_SYMBOL(out_of_line_wait_on_bit);
67 
out_of_line_wait_on_bit_timeout(void * word,int bit,wait_bit_action_f * action,unsigned mode,unsigned long timeout)68 int __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 }
79 EXPORT_SYMBOL_GPL(out_of_line_wait_on_bit_timeout);
80 
81 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)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 }
109 EXPORT_SYMBOL(__wait_on_bit_lock);
110 
out_of_line_wait_on_bit_lock(void * word,int bit,wait_bit_action_f * action,unsigned mode)111 int __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 }
119 EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);
120 
__wake_up_bit(struct wait_queue_head * wq_head,void * word,int bit)121 void __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 }
128 EXPORT_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  */
wake_up_bit(void * word,int bit)147 void wake_up_bit(void *word, int bit)
148 {
149 	__wake_up_bit(bit_waitqueue(word, bit), word, bit);
150 }
151 EXPORT_SYMBOL(wake_up_bit);
152 
__var_waitqueue(void * p)153 wait_queue_head_t *__var_waitqueue(void *p)
154 {
155 	return bit_wait_table + hash_ptr(p, WAIT_TABLE_BITS);
156 }
157 EXPORT_SYMBOL(__var_waitqueue);
158 
159 static int
var_wake_function(struct wait_queue_entry * wq_entry,unsigned int mode,int sync,void * arg)160 var_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 
init_wait_var_entry(struct wait_bit_queue_entry * wbq_entry,void * var,int flags)174 void 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 }
189 EXPORT_SYMBOL(init_wait_var_entry);
190 
wake_up_var(void * var)191 void wake_up_var(void *var)
192 {
193 	__wake_up_bit(__var_waitqueue(var), var, -1);
194 }
195 EXPORT_SYMBOL(wake_up_var);
196 
bit_wait(struct wait_bit_key * word,int mode)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 }
205 EXPORT_SYMBOL(bit_wait);
206 
bit_wait_io(struct wait_bit_key * word,int mode)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 }
215 EXPORT_SYMBOL(bit_wait_io);
216 
bit_wait_timeout(struct wait_bit_key * word,int mode)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 }
229 EXPORT_SYMBOL_GPL(bit_wait_timeout);
230 
bit_wait_io_timeout(struct wait_bit_key * word,int mode)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 }
243 EXPORT_SYMBOL_GPL(bit_wait_io_timeout);
244 
wait_bit_init(void)245 void __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