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(unsigned long *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. non-blocking)
  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(unsigned long *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         unsigned long *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(unsigned long *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, unsigned long *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 waiters on a bit
 132  * @word: the address containing the bit being waited on
 133  * @bit: the bit at that address being waited on
 134  *
 135  * Wake up any process waiting in wait_on_bit() or similar for the
 136  * given bit to be cleared.
 137  *
 138  * The wake-up is sent to tasks in a waitqueue selected by hash from a
 139  * shared pool.  Only those tasks on that queue which have requested
 140  * wake_up on this specific address and bit will be woken, and only if the
 141  * bit is clear.
 142  *
 143  * In order for this to function properly there must be a full memory
 144  * barrier after the bit is cleared and before this function is called.
 145  * If the bit was cleared atomically, such as a by clear_bit() then
 146  * smb_mb__after_atomic() can be used, othwewise smb_mb() is needed.
 147  * If the bit was cleared with a fully-ordered operation, no further
 148  * barrier is required.
 149  *
 150  * Normally the bit should be cleared by an operation with RELEASE
 151  * semantics so that any changes to memory made before the bit is
 152  * cleared are guaranteed to be visible after the matching wait_on_bit()
 153  * completes.
 154  */
 155 void wake_up_bit(unsigned long *word, int bit)
 156 {
 157         __wake_up_bit(bit_waitqueue(word, bit), word, bit);
 158 }
 159 EXPORT_SYMBOL(wake_up_bit);
 160
 161 wait_queue_head_t *__var_waitqueue(void *p)
 162 {
 163         return bit_wait_table + hash_ptr(p, WAIT_TABLE_BITS);
 164 }
 165 EXPORT_SYMBOL(__var_waitqueue);
 166
 167 static int
 168 var_wake_function(struct wait_queue_entry *wq_entry, unsigned int mode,
 169                   int sync, void *arg)
 170 {
 171         struct wait_bit_key *key = arg;
 172         struct wait_bit_queue_entry *wbq_entry =
 173                 container_of(wq_entry, struct wait_bit_queue_entry, wq_entry);
 174
 175         if (wbq_entry->key.flags != key->flags ||
 176             wbq_entry->key.bit_nr != key->bit_nr)
 177                 return 0;
 178
 179         return autoremove_wake_function(wq_entry, mode, sync, key);
 180 }
 181
 182 void init_wait_var_entry(struct wait_bit_queue_entry *wbq_entry, void *var, int flags)
 183 {
 184         *wbq_entry = (struct wait_bit_queue_entry){
 185                 .key = {
 186                         .flags  = (var),
 187                         .bit_nr = -1,
 188                 },
 189                 .wq_entry = {
 190                         .flags   = flags,
 191                         .private = current,
 192                         .func    = var_wake_function,
 193                         .entry   = LIST_HEAD_INIT(wbq_entry->wq_entry.entry),
 194                 },
 195         };
 196 }
 197 EXPORT_SYMBOL(init_wait_var_entry);
 198
 199 /**
 200  * wake_up_var - wake up waiters on a variable (kernel address)
 201  * @var: the address of the variable being waited on
 202  *
 203  * Wake up any process waiting in wait_var_event() or similar for the
 204  * given variable to change.  wait_var_event() can be waiting for an
 205  * arbitrary condition to be true and associates that condition with an
 206  * address.  Calling wake_up_var() suggests that the condition has been
 207  * made true, but does not strictly require the condtion to use the
 208  * address given.
 209  *
 210  * The wake-up is sent to tasks in a waitqueue selected by hash from a
 211  * shared pool.  Only those tasks on that queue which have requested
 212  * wake_up on this specific address will be woken.
 213  *
 214  * In order for this to function properly there must be a full memory
 215  * barrier after the variable is updated (or more accurately, after the
 216  * condition waited on has been made to be true) and before this function
 217  * is called.  If the variable was updated atomically, such as a by
 218  * atomic_dec() then smb_mb__after_atomic() can be used.  If the
 219  * variable was updated by a fully ordered operation such as
 220  * atomic_dec_and_test() then no extra barrier is required.  Otherwise
 221  * smb_mb() is needed.
 222  *
 223  * Normally the variable should be updated (the condition should be made
 224  * to be true) by an operation with RELEASE semantics such as
 225  * smp_store_release() so that any changes to memory made before the
 226  * variable was updated are guaranteed to be visible after the matching
 227  * wait_var_event() completes.
 228  */
 229 void wake_up_var(void *var)
 230 {
 231         __wake_up_bit(__var_waitqueue(var), var, -1);
 232 }
 233 EXPORT_SYMBOL(wake_up_var);
 234
 235 __sched int bit_wait(struct wait_bit_key *word, int mode)
 236 {
 237         schedule();
 238         if (signal_pending_state(mode, current))
 239                 return -EINTR;
 240
 241         return 0;
 242 }
 243 EXPORT_SYMBOL(bit_wait);
 244
 245 __sched int bit_wait_io(struct wait_bit_key *word, int mode)
 246 {
 247         io_schedule();
 248         if (signal_pending_state(mode, current))
 249                 return -EINTR;
 250
 251         return 0;
 252 }
 253 EXPORT_SYMBOL(bit_wait_io);
 254
 255 __sched int bit_wait_timeout(struct wait_bit_key *word, int mode)
 256 {
 257         unsigned long now = READ_ONCE(jiffies);
 258
 259         if (time_after_eq(now, word->timeout))
 260                 return -EAGAIN;
 261         schedule_timeout(word->timeout - now);
 262         if (signal_pending_state(mode, current))
 263                 return -EINTR;
 264
 265         return 0;
 266 }
 267 EXPORT_SYMBOL_GPL(bit_wait_timeout);
 268
 269 void __init wait_bit_init(void)
 270 {
 271         int i;
 272
 273         for (i = 0; i < WAIT_TABLE_SIZE; i++)
 274                 init_waitqueue_head(bit_wait_table + i);
 275 }