kernel/sched/wait_bit.c

0001 // SPDX-License-Identifier: GPL-2.0-only
0002
0003 /*
0004  * The implementation of the wait_bit*() and related waiting APIs:
0005  */
0006
0007 #define WAIT_TABLE_BITS 8
0008 #define WAIT_TABLE_SIZE (1 << WAIT_TABLE_BITS)
0009
0010 static wait_queue_head_t bit_wait_table[WAIT_TABLE_SIZE] __cacheline_aligned;
0011
0012 wait_queue_head_t *bit_waitqueue(void *word, int bit)
0013 {
0014     const int shift = BITS_PER_LONG == 32 ? 5 : 6;
0015     unsigned long val = (unsigned long)word << shift | bit;
0016
0017     return bit_wait_table + hash_long(val, WAIT_TABLE_BITS);
0018 }
0019 EXPORT_SYMBOL(bit_waitqueue);
0020
0021 int wake_bit_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *arg)
0022 {
0023     struct wait_bit_key *key = arg;
0024     struct wait_bit_queue_entry *wait_bit = container_of(wq_entry, struct wait_bit_queue_entry, wq_entry);
0025
0026     if (wait_bit->key.flags != key->flags ||
0027             wait_bit->key.bit_nr != key->bit_nr ||
0028             test_bit(key->bit_nr, key->flags))
0029         return 0;
0030
0031     return autoremove_wake_function(wq_entry, mode, sync, key);
0032 }
0033 EXPORT_SYMBOL(wake_bit_function);
0034
0035 /*
0036  * To allow interruptible waiting and asynchronous (i.e. nonblocking)
0037  * waiting, the actions of __wait_on_bit() and __wait_on_bit_lock() are
0038  * permitted return codes. Nonzero return codes halt waiting and return.
0039  */
0040 int __sched
0041 __wait_on_bit(struct wait_queue_head *wq_head, struct wait_bit_queue_entry *wbq_entry,
0042           wait_bit_action_f *action, unsigned mode)
0043 {
0044     int ret = 0;
0045
0046     do {
0047         prepare_to_wait(wq_head, &wbq_entry->wq_entry, mode);
0048         if (test_bit(wbq_entry->key.bit_nr, wbq_entry->key.flags))
0049             ret = (*action)(&wbq_entry->key, mode);
0050     } while (test_bit_acquire(wbq_entry->key.bit_nr, wbq_entry->key.flags) && !ret);
0051
0052     finish_wait(wq_head, &wbq_entry->wq_entry);
0053
0054     return ret;
0055 }
0056 EXPORT_SYMBOL(__wait_on_bit);
0057
0058 int __sched out_of_line_wait_on_bit(void *word, int bit,
0059                     wait_bit_action_f *action, unsigned mode)
0060 {
0061     struct wait_queue_head *wq_head = bit_waitqueue(word, bit);
0062     DEFINE_WAIT_BIT(wq_entry, word, bit);
0063
0064     return __wait_on_bit(wq_head, &wq_entry, action, mode);
0065 }
0066 EXPORT_SYMBOL(out_of_line_wait_on_bit);
0067
0068 int __sched out_of_line_wait_on_bit_timeout(
0069     void *word, int bit, wait_bit_action_f *action,
0070     unsigned mode, unsigned long timeout)
0071 {
0072     struct wait_queue_head *wq_head = bit_waitqueue(word, bit);
0073     DEFINE_WAIT_BIT(wq_entry, word, bit);
0074
0075     wq_entry.key.timeout = jiffies + timeout;
0076
0077     return __wait_on_bit(wq_head, &wq_entry, action, mode);
0078 }
0079 EXPORT_SYMBOL_GPL(out_of_line_wait_on_bit_timeout);
0080
0081 int __sched
0082 __wait_on_bit_lock(struct wait_queue_head *wq_head, struct wait_bit_queue_entry *wbq_entry,
0083             wait_bit_action_f *action, unsigned mode)
0084 {
0085     int ret = 0;
0086
0087     for (;;) {
0088         prepare_to_wait_exclusive(wq_head, &wbq_entry->wq_entry, mode);
0089         if (test_bit(wbq_entry->key.bit_nr, wbq_entry->key.flags)) {
0090             ret = action(&wbq_entry->key, mode);
0091             /*
0092              * See the comment in prepare_to_wait_event().
0093              * finish_wait() does not necessarily takes wwq_head->lock,
0094              * but test_and_set_bit() implies mb() which pairs with
0095              * smp_mb__after_atomic() before wake_up_page().
0096              */
0097             if (ret)
0098                 finish_wait(wq_head, &wbq_entry->wq_entry);
0099         }
0100         if (!test_and_set_bit(wbq_entry->key.bit_nr, wbq_entry->key.flags)) {
0101             if (!ret)
0102                 finish_wait(wq_head, &wbq_entry->wq_entry);
0103             return 0;
0104         } else if (ret) {
0105             return ret;
0106         }
0107     }
0108 }
0109 EXPORT_SYMBOL(__wait_on_bit_lock);
0110
0111 int __sched out_of_line_wait_on_bit_lock(void *word, int bit,
0112                      wait_bit_action_f *action, unsigned mode)
0113 {
0114     struct wait_queue_head *wq_head = bit_waitqueue(word, bit);
0115     DEFINE_WAIT_BIT(wq_entry, word, bit);
0116
0117     return __wait_on_bit_lock(wq_head, &wq_entry, action, mode);
0118 }
0119 EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);
0120
0121 void __wake_up_bit(struct wait_queue_head *wq_head, void *word, int bit)
0122 {
0123     struct wait_bit_key key = __WAIT_BIT_KEY_INITIALIZER(word, bit);
0124
0125     if (waitqueue_active(wq_head))
0126         __wake_up(wq_head, TASK_NORMAL, 1, &key);
0127 }
0128 EXPORT_SYMBOL(__wake_up_bit);
0129
0130 /**
0131  * wake_up_bit - wake up a waiter on a bit
0132  * @word: the word being waited on, a kernel virtual address
0133  * @bit: the bit of the word being waited on
0134  *
0135  * There is a standard hashed waitqueue table for generic use. This
0136  * is the part of the hashtable's accessor API that wakes up waiters
0137  * on a bit. For instance, if one were to have waiters on a bitflag,
0138  * one would call wake_up_bit() after clearing the bit.
0139  *
0140  * In order for this to function properly, as it uses waitqueue_active()
0141  * internally, some kind of memory barrier must be done prior to calling
0142  * this. Typically, this will be smp_mb__after_atomic(), but in some
0143  * cases where bitflags are manipulated non-atomically under a lock, one
0144  * may need to use a less regular barrier, such fs/inode.c's smp_mb(),
0145  * because spin_unlock() does not guarantee a memory barrier.
0146  */
0147 void wake_up_bit(void *word, int bit)
0148 {
0149     __wake_up_bit(bit_waitqueue(word, bit), word, bit);
0150 }
0151 EXPORT_SYMBOL(wake_up_bit);
0152
0153 wait_queue_head_t *__var_waitqueue(void *p)
0154 {
0155     return bit_wait_table + hash_ptr(p, WAIT_TABLE_BITS);
0156 }
0157 EXPORT_SYMBOL(__var_waitqueue);
0158
0159 static int
0160 var_wake_function(struct wait_queue_entry *wq_entry, unsigned int mode,
0161           int sync, void *arg)
0162 {
0163     struct wait_bit_key *key = arg;
0164     struct wait_bit_queue_entry *wbq_entry =
0165         container_of(wq_entry, struct wait_bit_queue_entry, wq_entry);
0166
0167     if (wbq_entry->key.flags != key->flags ||
0168         wbq_entry->key.bit_nr != key->bit_nr)
0169         return 0;
0170
0171     return autoremove_wake_function(wq_entry, mode, sync, key);
0172 }
0173
0174 void init_wait_var_entry(struct wait_bit_queue_entry *wbq_entry, void *var, int flags)
0175 {
0176     *wbq_entry = (struct wait_bit_queue_entry){
0177         .key = {
0178             .flags  = (var),
0179             .bit_nr = -1,
0180         },
0181         .wq_entry = {
0182             .flags   = flags,
0183             .private = current,
0184             .func    = var_wake_function,
0185             .entry   = LIST_HEAD_INIT(wbq_entry->wq_entry.entry),
0186         },
0187     };
0188 }
0189 EXPORT_SYMBOL(init_wait_var_entry);
0190
0191 void wake_up_var(void *var)
0192 {
0193     __wake_up_bit(__var_waitqueue(var), var, -1);
0194 }
0195 EXPORT_SYMBOL(wake_up_var);
0196
0197 __sched int bit_wait(struct wait_bit_key *word, int mode)
0198 {
0199     schedule();
0200     if (signal_pending_state(mode, current))
0201         return -EINTR;
0202
0203     return 0;
0204 }
0205 EXPORT_SYMBOL(bit_wait);
0206
0207 __sched int bit_wait_io(struct wait_bit_key *word, int mode)
0208 {
0209     io_schedule();
0210     if (signal_pending_state(mode, current))
0211         return -EINTR;
0212
0213     return 0;
0214 }
0215 EXPORT_SYMBOL(bit_wait_io);
0216
0217 __sched int bit_wait_timeout(struct wait_bit_key *word, int mode)
0218 {
0219     unsigned long now = READ_ONCE(jiffies);
0220
0221     if (time_after_eq(now, word->timeout))
0222         return -EAGAIN;
0223     schedule_timeout(word->timeout - now);
0224     if (signal_pending_state(mode, current))
0225         return -EINTR;
0226
0227     return 0;
0228 }
0229 EXPORT_SYMBOL_GPL(bit_wait_timeout);
0230
0231 __sched int bit_wait_io_timeout(struct wait_bit_key *word, int mode)
0232 {
0233     unsigned long now = READ_ONCE(jiffies);
0234
0235     if (time_after_eq(now, word->timeout))
0236         return -EAGAIN;
0237     io_schedule_timeout(word->timeout - now);
0238     if (signal_pending_state(mode, current))
0239         return -EINTR;
0240
0241     return 0;
0242 }
0243 EXPORT_SYMBOL_GPL(bit_wait_io_timeout);
0244
0245 void __init wait_bit_init(void)
0246 {
0247     int i;
0248
0249     for (i = 0; i < WAIT_TABLE_SIZE; i++)
0250         init_waitqueue_head(bit_wait_table + i);
0251 }