wait.c

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/*
 * Generic waiting primitives.
 *
 * (C) 2004 William Irwin, Oracle
 */
#include <linux/init.h>
#include <linux/export.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/wait.h>
#include <linux/hash.h>

void __init_waitqueue_head(wait_queue_head_t *q, const char *name, struct lock_class_key *key)
{
    spin_lock_init(&q->lock);
    lockdep_set_class_and_name(&q->lock, key, name);
    INIT_LIST_HEAD(&q->task_list);
}

EXPORT_SYMBOL(__init_waitqueue_head);

void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
{
    unsigned long flags;

    wait->flags &= ~WQ_FLAG_EXCLUSIVE;
    spin_lock_irqsave(&q->lock, flags);
    __add_wait_queue(q, wait);
    spin_unlock_irqrestore(&q->lock, flags);
}
EXPORT_SYMBOL(add_wait_queue);

void add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait)
{
    unsigned long flags;

    wait->flags |= WQ_FLAG_EXCLUSIVE;
    spin_lock_irqsave(&q->lock, flags);
    __add_wait_queue_tail(q, wait);
    spin_unlock_irqrestore(&q->lock, flags);
}
EXPORT_SYMBOL(add_wait_queue_exclusive);

void remove_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
{
    unsigned long flags;

    spin_lock_irqsave(&q->lock, flags);
    __remove_wait_queue(q, wait);
    spin_unlock_irqrestore(&q->lock, flags);
}
EXPORT_SYMBOL(remove_wait_queue);


/*
 * Note: we use "set_current_state()" _after_ the wait-queue add,
 * because we need a memory barrier there on SMP, so that any
 * wake-function that tests for the wait-queue being active
 * will be guaranteed to see waitqueue addition _or_ subsequent
 * tests in this thread will see the wakeup having taken place.
 *
 * The spin_unlock() itself is semi-permeable and only protects
 * one way (it only protects stuff inside the critical region and
 * stops them from bleeding out - it would still allow subsequent
 * loads to move into the critical region).
 */
void
prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, int state)
{
    unsigned long flags;

    wait->flags &= ~WQ_FLAG_EXCLUSIVE;
    spin_lock_irqsave(&q->lock, flags);
    if (list_empty(&wait->task_list))
        __add_wait_queue(q, wait);
    set_current_state(state);
    spin_unlock_irqrestore(&q->lock, flags);
}
EXPORT_SYMBOL(prepare_to_wait);

void
prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state)
{
    unsigned long flags;

    wait->flags |= WQ_FLAG_EXCLUSIVE;
    spin_lock_irqsave(&q->lock, flags);
    if (list_empty(&wait->task_list))
        __add_wait_queue_tail(q, wait);
    set_current_state(state);
    spin_unlock_irqrestore(&q->lock, flags);
}
EXPORT_SYMBOL(prepare_to_wait_exclusive);

void finish_wait(wait_queue_head_t *q, wait_queue_t *wait)
{
    unsigned long flags;

    __set_current_state(TASK_RUNNING);
    /*
     * We can check for list emptiness outside the lock
     * IFF:
     *  - we use the "careful" check that verifies both
     *    the next and prev pointers, so that there cannot
     *    be any half-pending updates in progress on other
     *    CPU's that we haven't seen yet (and that might
     *    still change the stack area.
     * and
     *  - all other users take the lock (ie we can only
     *    have _one_ other CPU that looks at or modifies
     *    the list).
     */
    if (!list_empty_careful(&wait->task_list)) {
        spin_lock_irqsave(&q->lock, flags);
        list_del_init(&wait->task_list);
        spin_unlock_irqrestore(&q->lock, flags);
    }
}
EXPORT_SYMBOL(finish_wait);

void abort_exclusive_wait(wait_queue_head_t *q, wait_queue_t *wait,
            unsigned int mode, void *key)
{
    unsigned long flags;

    __set_current_state(TASK_RUNNING);
    spin_lock_irqsave(&q->lock, flags);
    if (!list_empty(&wait->task_list))
        list_del_init(&wait->task_list);
    else if (waitqueue_active(q))
        __wake_up_locked_key(q, mode, key);
    spin_unlock_irqrestore(&q->lock, flags);
}
EXPORT_SYMBOL(abort_exclusive_wait);

int autoremove_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
{
    int ret = default_wake_function(wait, mode, sync, key);

    if (ret)
        list_del_init(&wait->task_list);
    return ret;
}
EXPORT_SYMBOL(autoremove_wake_function);

int wake_bit_function(wait_queue_t *wait, unsigned mode, int sync, void *arg)
{
    struct wait_bit_key *key = arg;
    struct wait_bit_queue *wait_bit
        = container_of(wait, struct wait_bit_queue, wait);

    if (wait_bit->key.flags != key->flags ||
            wait_bit->key.bit_nr != key->bit_nr ||
            test_bit(key->bit_nr, key->flags))
        return 0;
    else
        return autoremove_wake_function(wait, mode, sync, key);
}
EXPORT_SYMBOL(wake_bit_function);

/*
 * To allow interruptible waiting and asynchronous (i.e. nonblocking)
 * waiting, the actions of __wait_on_bit() and __wait_on_bit_lock() are
 * permitted return codes. Nonzero return codes halt waiting and return.
 */
int __sched
__wait_on_bit(wait_queue_head_t *wq, struct wait_bit_queue *q,
            int (*action)(void *), unsigned mode)
{
    int ret = 0;

    do {
        prepare_to_wait(wq, &q->wait, mode);
        if (test_bit(q->key.bit_nr, q->key.flags))
            ret = (*action)(q->key.flags);
    } while (test_bit(q->key.bit_nr, q->key.flags) && !ret);
    finish_wait(wq, &q->wait);
    return ret;
}
EXPORT_SYMBOL(__wait_on_bit);

int __sched out_of_line_wait_on_bit(void *word, int bit,
                    int (*action)(void *), unsigned mode)
{
    wait_queue_head_t *wq = bit_waitqueue(word, bit);
    DEFINE_WAIT_BIT(wait, word, bit);

    return __wait_on_bit(wq, &wait, action, mode);
}
EXPORT_SYMBOL(out_of_line_wait_on_bit);

int __sched
__wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
            int (*action)(void *), unsigned mode)
{
    do {
        int ret;

        prepare_to_wait_exclusive(wq, &q->wait, mode);
        if (!test_bit(q->key.bit_nr, q->key.flags))
            continue;
        ret = action(q->key.flags);
        if (!ret)
            continue;
        abort_exclusive_wait(wq, &q->wait, mode, &q->key);
        return ret;
    } while (test_and_set_bit(q->key.bit_nr, q->key.flags));
    finish_wait(wq, &q->wait);
    return 0;
}
EXPORT_SYMBOL(__wait_on_bit_lock);

int __sched out_of_line_wait_on_bit_lock(void *word, int bit,
                    int (*action)(void *), unsigned mode)
{
    wait_queue_head_t *wq = bit_waitqueue(word, bit);
    DEFINE_WAIT_BIT(wait, word, bit);

    return __wait_on_bit_lock(wq, &wait, action, mode);
}
EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);

void __wake_up_bit(wait_queue_head_t *wq, void *word, int bit)
{
    struct wait_bit_key key = __WAIT_BIT_KEY_INITIALIZER(word, bit);
    if (waitqueue_active(wq))
        __wake_up(wq, TASK_NORMAL, 1, &key);
}
EXPORT_SYMBOL(__wake_up_bit);

void wake_up_bit(void *word, int bit)
{
    __wake_up_bit(bit_waitqueue(word, bit), word, bit);
}
EXPORT_SYMBOL(wake_up_bit);

wait_queue_head_t *bit_waitqueue(void *word, int bit)
{
    const int shift = BITS_PER_LONG == 32 ? 5 : 6;
    const struct zone *zone = page_zone(virt_to_page(word));
    unsigned long val = (unsigned long)word << shift | bit;

    return &zone->wait_table[hash_long(val, zone->wait_table_bits)];
}
EXPORT_SYMBOL(bit_waitqueue);