linux/kernel/wait.c
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   1/*
   2 * Generic waiting primitives.
   3 *
   4 * (C) 2004 Nadia Yvette Chambers, Oracle
   5 */
   6#include <linux/init.h>
   7#include <linux/export.h>
   8#include <linux/sched.h>
   9#include <linux/mm.h>
  10#include <linux/wait.h>
  11#include <linux/hash.h>
  12
  13void __init_waitqueue_head(wait_queue_head_t *q, const char *name, struct lock_class_key *key)
  14{
  15        spin_lock_init(&q->lock);
  16        lockdep_set_class_and_name(&q->lock, key, name);
  17        INIT_LIST_HEAD(&q->task_list);
  18}
  19
  20EXPORT_SYMBOL(__init_waitqueue_head);
  21
  22void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
  23{
  24        unsigned long flags;
  25
  26        wait->flags &= ~WQ_FLAG_EXCLUSIVE;
  27        spin_lock_irqsave(&q->lock, flags);
  28        __add_wait_queue(q, wait);
  29        spin_unlock_irqrestore(&q->lock, flags);
  30}
  31EXPORT_SYMBOL(add_wait_queue);
  32
  33void add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait)
  34{
  35        unsigned long flags;
  36
  37        wait->flags |= WQ_FLAG_EXCLUSIVE;
  38        spin_lock_irqsave(&q->lock, flags);
  39        __add_wait_queue_tail(q, wait);
  40        spin_unlock_irqrestore(&q->lock, flags);
  41}
  42EXPORT_SYMBOL(add_wait_queue_exclusive);
  43
  44void remove_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
  45{
  46        unsigned long flags;
  47
  48        spin_lock_irqsave(&q->lock, flags);
  49        __remove_wait_queue(q, wait);
  50        spin_unlock_irqrestore(&q->lock, flags);
  51}
  52EXPORT_SYMBOL(remove_wait_queue);
  53
  54
  55/*
  56 * Note: we use "set_current_state()" _after_ the wait-queue add,
  57 * because we need a memory barrier there on SMP, so that any
  58 * wake-function that tests for the wait-queue being active
  59 * will be guaranteed to see waitqueue addition _or_ subsequent
  60 * tests in this thread will see the wakeup having taken place.
  61 *
  62 * The spin_unlock() itself is semi-permeable and only protects
  63 * one way (it only protects stuff inside the critical region and
  64 * stops them from bleeding out - it would still allow subsequent
  65 * loads to move into the critical region).
  66 */
  67void
  68prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, int state)
  69{
  70        unsigned long flags;
  71
  72        wait->flags &= ~WQ_FLAG_EXCLUSIVE;
  73        spin_lock_irqsave(&q->lock, flags);
  74        if (list_empty(&wait->task_list))
  75                __add_wait_queue(q, wait);
  76        set_current_state(state);
  77        spin_unlock_irqrestore(&q->lock, flags);
  78}
  79EXPORT_SYMBOL(prepare_to_wait);
  80
  81void
  82prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state)
  83{
  84        unsigned long flags;
  85
  86        wait->flags |= WQ_FLAG_EXCLUSIVE;
  87        spin_lock_irqsave(&q->lock, flags);
  88        if (list_empty(&wait->task_list))
  89                __add_wait_queue_tail(q, wait);
  90        set_current_state(state);
  91        spin_unlock_irqrestore(&q->lock, flags);
  92}
  93EXPORT_SYMBOL(prepare_to_wait_exclusive);
  94
  95/**
  96 * finish_wait - clean up after waiting in a queue
  97 * @q: waitqueue waited on
  98 * @wait: wait descriptor
  99 *
 100 * Sets current thread back to running state and removes
 101 * the wait descriptor from the given waitqueue if still
 102 * queued.
 103 */
 104void finish_wait(wait_queue_head_t *q, wait_queue_t *wait)
 105{
 106        unsigned long flags;
 107
 108        __set_current_state(TASK_RUNNING);
 109        /*
 110         * We can check for list emptiness outside the lock
 111         * IFF:
 112         *  - we use the "careful" check that verifies both
 113         *    the next and prev pointers, so that there cannot
 114         *    be any half-pending updates in progress on other
 115         *    CPU's that we haven't seen yet (and that might
 116         *    still change the stack area.
 117         * and
 118         *  - all other users take the lock (ie we can only
 119         *    have _one_ other CPU that looks at or modifies
 120         *    the list).
 121         */
 122        if (!list_empty_careful(&wait->task_list)) {
 123                spin_lock_irqsave(&q->lock, flags);
 124                list_del_init(&wait->task_list);
 125                spin_unlock_irqrestore(&q->lock, flags);
 126        }
 127}
 128EXPORT_SYMBOL(finish_wait);
 129
 130/**
 131 * abort_exclusive_wait - abort exclusive waiting in a queue
 132 * @q: waitqueue waited on
 133 * @wait: wait descriptor
 134 * @mode: runstate of the waiter to be woken
 135 * @key: key to identify a wait bit queue or %NULL
 136 *
 137 * Sets current thread back to running state and removes
 138 * the wait descriptor from the given waitqueue if still
 139 * queued.
 140 *
 141 * Wakes up the next waiter if the caller is concurrently
 142 * woken up through the queue.
 143 *
 144 * This prevents waiter starvation where an exclusive waiter
 145 * aborts and is woken up concurrently and no one wakes up
 146 * the next waiter.
 147 */
 148void abort_exclusive_wait(wait_queue_head_t *q, wait_queue_t *wait,
 149                        unsigned int mode, void *key)
 150{
 151        unsigned long flags;
 152
 153        __set_current_state(TASK_RUNNING);
 154        spin_lock_irqsave(&q->lock, flags);
 155        if (!list_empty(&wait->task_list))
 156                list_del_init(&wait->task_list);
 157        else if (waitqueue_active(q))
 158                __wake_up_locked_key(q, mode, key);
 159        spin_unlock_irqrestore(&q->lock, flags);
 160}
 161EXPORT_SYMBOL(abort_exclusive_wait);
 162
 163int autoremove_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
 164{
 165        int ret = default_wake_function(wait, mode, sync, key);
 166
 167        if (ret)
 168                list_del_init(&wait->task_list);
 169        return ret;
 170}
 171EXPORT_SYMBOL(autoremove_wake_function);
 172
 173int wake_bit_function(wait_queue_t *wait, unsigned mode, int sync, void *arg)
 174{
 175        struct wait_bit_key *key = arg;
 176        struct wait_bit_queue *wait_bit
 177                = container_of(wait, struct wait_bit_queue, wait);
 178
 179        if (wait_bit->key.flags != key->flags ||
 180                        wait_bit->key.bit_nr != key->bit_nr ||
 181                        test_bit(key->bit_nr, key->flags))
 182                return 0;
 183        else
 184                return autoremove_wake_function(wait, mode, sync, key);
 185}
 186EXPORT_SYMBOL(wake_bit_function);
 187
 188/*
 189 * To allow interruptible waiting and asynchronous (i.e. nonblocking)
 190 * waiting, the actions of __wait_on_bit() and __wait_on_bit_lock() are
 191 * permitted return codes. Nonzero return codes halt waiting and return.
 192 */
 193int __sched
 194__wait_on_bit(wait_queue_head_t *wq, struct wait_bit_queue *q,
 195                        int (*action)(void *), unsigned mode)
 196{
 197        int ret = 0;
 198
 199        do {
 200                prepare_to_wait(wq, &q->wait, mode);
 201                if (test_bit(q->key.bit_nr, q->key.flags))
 202                        ret = (*action)(q->key.flags);
 203        } while (test_bit(q->key.bit_nr, q->key.flags) && !ret);
 204        finish_wait(wq, &q->wait);
 205        return ret;
 206}
 207EXPORT_SYMBOL(__wait_on_bit);
 208
 209int __sched out_of_line_wait_on_bit(void *word, int bit,
 210                                        int (*action)(void *), unsigned mode)
 211{
 212        wait_queue_head_t *wq = bit_waitqueue(word, bit);
 213        DEFINE_WAIT_BIT(wait, word, bit);
 214
 215        return __wait_on_bit(wq, &wait, action, mode);
 216}
 217EXPORT_SYMBOL(out_of_line_wait_on_bit);
 218
 219int __sched
 220__wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
 221                        int (*action)(void *), unsigned mode)
 222{
 223        do {
 224                int ret;
 225
 226                prepare_to_wait_exclusive(wq, &q->wait, mode);
 227                if (!test_bit(q->key.bit_nr, q->key.flags))
 228                        continue;
 229                ret = action(q->key.flags);
 230                if (!ret)
 231                        continue;
 232                abort_exclusive_wait(wq, &q->wait, mode, &q->key);
 233                return ret;
 234        } while (test_and_set_bit(q->key.bit_nr, q->key.flags));
 235        finish_wait(wq, &q->wait);
 236        return 0;
 237}
 238EXPORT_SYMBOL(__wait_on_bit_lock);
 239
 240int __sched out_of_line_wait_on_bit_lock(void *word, int bit,
 241                                        int (*action)(void *), unsigned mode)
 242{
 243        wait_queue_head_t *wq = bit_waitqueue(word, bit);
 244        DEFINE_WAIT_BIT(wait, word, bit);
 245
 246        return __wait_on_bit_lock(wq, &wait, action, mode);
 247}
 248EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);
 249
 250void __wake_up_bit(wait_queue_head_t *wq, void *word, int bit)
 251{
 252        struct wait_bit_key key = __WAIT_BIT_KEY_INITIALIZER(word, bit);
 253        if (waitqueue_active(wq))
 254                __wake_up(wq, TASK_NORMAL, 1, &key);
 255}
 256EXPORT_SYMBOL(__wake_up_bit);
 257
 258/**
 259 * wake_up_bit - wake up a waiter on a bit
 260 * @word: the word being waited on, a kernel virtual address
 261 * @bit: the bit of the word being waited on
 262 *
 263 * There is a standard hashed waitqueue table for generic use. This
 264 * is the part of the hashtable's accessor API that wakes up waiters
 265 * on a bit. For instance, if one were to have waiters on a bitflag,
 266 * one would call wake_up_bit() after clearing the bit.
 267 *
 268 * In order for this to function properly, as it uses waitqueue_active()
 269 * internally, some kind of memory barrier must be done prior to calling
 270 * this. Typically, this will be smp_mb__after_clear_bit(), but in some
 271 * cases where bitflags are manipulated non-atomically under a lock, one
 272 * may need to use a less regular barrier, such fs/inode.c's smp_mb(),
 273 * because spin_unlock() does not guarantee a memory barrier.
 274 */
 275void wake_up_bit(void *word, int bit)
 276{
 277        __wake_up_bit(bit_waitqueue(word, bit), word, bit);
 278}
 279EXPORT_SYMBOL(wake_up_bit);
 280
 281wait_queue_head_t *bit_waitqueue(void *word, int bit)
 282{
 283        const int shift = BITS_PER_LONG == 32 ? 5 : 6;
 284        const struct zone *zone = page_zone(virt_to_page(word));
 285        unsigned long val = (unsigned long)word << shift | bit;
 286
 287        return &zone->wait_table[hash_long(val, zone->wait_table_bits)];
 288}
 289EXPORT_SYMBOL(bit_waitqueue);
 290
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