kernel/sched/wait_bit.c

   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
  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
  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
  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
  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
  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
  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
 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
 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  */
 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
 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
 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
 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
 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
 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
 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
 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
 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
 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 }