[people/arne_f/kernel.git] / kernel / sched / wait.c

/*
 * Generic waiting primitives.
 *
 * (C) 2004 Nadia Yvette Chambers, Oracle
 */
#include <linux/init.h>
#include <linux/export.h>
#include <linux/sched/signal.h>
#include <linux/sched/debug.h>
#include <linux/mm.h>
#include <linux/wait.h>
#include <linux/hash.h>
#include <linux/kthread.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, struct wait_queue_entry *wq_entry)
{
        unsigned long flags;

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

void add_wait_queue_exclusive(wait_queue_head_t *q, struct wait_queue_entry *wq_entry)
{
        unsigned long flags;

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

void remove_wait_queue(wait_queue_head_t *q, struct wait_queue_entry *wq_entry)
{
        unsigned long flags;

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


/*
 * The core wakeup function. Non-exclusive wakeups (nr_exclusive == 0) just
 * wake everything up. If it's an exclusive wakeup (nr_exclusive == small +ve
 * number) then we wake all the non-exclusive tasks and one exclusive task.
 *
 * There are circumstances in which we can try to wake a task which has already
 * started to run but is not in state TASK_RUNNING. try_to_wake_up() returns
 * zero in this (rare) case, and we handle it by continuing to scan the queue.
 */
static void __wake_up_common(wait_queue_head_t *q, unsigned int mode,
                        int nr_exclusive, int wake_flags, void *key)
{
        wait_queue_entry_t *curr, *next;

        list_for_each_entry_safe(curr, next, &q->task_list, task_list) {
                unsigned flags = curr->flags;

                if (curr->func(curr, mode, wake_flags, key) &&
                                (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
                        break;
        }
}

/**
 * __wake_up - wake up threads blocked on a waitqueue.
 * @q: the waitqueue
 * @mode: which threads
 * @nr_exclusive: how many wake-one or wake-many threads to wake up
 * @key: is directly passed to the wakeup function
 *
 * It may be assumed that this function implies a write memory barrier before
 * changing the task state if and only if any tasks are woken up.
 */
void __wake_up(wait_queue_head_t *q, unsigned int mode,
                        int nr_exclusive, void *key)
{
        unsigned long flags;

        spin_lock_irqsave(&q->lock, flags);
        __wake_up_common(q, mode, nr_exclusive, 0, key);
        spin_unlock_irqrestore(&q->lock, flags);
}
EXPORT_SYMBOL(__wake_up);

/*
 * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
 */
void __wake_up_locked(wait_queue_head_t *q, unsigned int mode, int nr)
{
        __wake_up_common(q, mode, nr, 0, NULL);
}
EXPORT_SYMBOL_GPL(__wake_up_locked);

void __wake_up_locked_key(wait_queue_head_t *q, unsigned int mode, void *key)
{
        __wake_up_common(q, mode, 1, 0, key);
}
EXPORT_SYMBOL_GPL(__wake_up_locked_key);

/**
 * __wake_up_sync_key - wake up threads blocked on a waitqueue.
 * @q: the waitqueue
 * @mode: which threads
 * @nr_exclusive: how many wake-one or wake-many threads to wake up
 * @key: opaque value to be passed to wakeup targets
 *
 * The sync wakeup differs that the waker knows that it will schedule
 * away soon, so while the target thread will be woken up, it will not
 * be migrated to another CPU - ie. the two threads are 'synchronized'
 * with each other. This can prevent needless bouncing between CPUs.
 *
 * On UP it can prevent extra preemption.
 *
 * It may be assumed that this function implies a write memory barrier before
 * changing the task state if and only if any tasks are woken up.
 */
void __wake_up_sync_key(wait_queue_head_t *q, unsigned int mode,
                        int nr_exclusive, void *key)
{
        unsigned long flags;
        int wake_flags = 1; /* XXX WF_SYNC */

        if (unlikely(!q))
                return;

        if (unlikely(nr_exclusive != 1))
                wake_flags = 0;

        spin_lock_irqsave(&q->lock, flags);
        __wake_up_common(q, mode, nr_exclusive, wake_flags, key);
        spin_unlock_irqrestore(&q->lock, flags);
}
EXPORT_SYMBOL_GPL(__wake_up_sync_key);

/*
 * __wake_up_sync - see __wake_up_sync_key()
 */
void __wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr_exclusive)
{
        __wake_up_sync_key(q, mode, nr_exclusive, NULL);
}
EXPORT_SYMBOL_GPL(__wake_up_sync);      /* For internal use only */

/*
 * 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, struct wait_queue_entry *wq_entry, int state)
{
        unsigned long flags;

        wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
        spin_lock_irqsave(&q->lock, flags);
        if (list_empty(&wq_entry->task_list))
                __add_wait_queue(q, wq_entry);
        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, struct wait_queue_entry *wq_entry, int state)
{
        unsigned long flags;

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

void init_wait_entry(struct wait_queue_entry *wq_entry, int flags)
{
        wq_entry->flags = flags;
        wq_entry->private = current;
        wq_entry->func = autoremove_wake_function;
        INIT_LIST_HEAD(&wq_entry->task_list);
}
EXPORT_SYMBOL(init_wait_entry);

long prepare_to_wait_event(wait_queue_head_t *q, struct wait_queue_entry *wq_entry, int state)
{
        unsigned long flags;
        long ret = 0;

        spin_lock_irqsave(&q->lock, flags);
        if (unlikely(signal_pending_state(state, current))) {
                /*
                 * Exclusive waiter must not fail if it was selected by wakeup,
                 * it should "consume" the condition we were waiting for.
                 *
                 * The caller will recheck the condition and return success if
                 * we were already woken up, we can not miss the event because
                 * wakeup locks/unlocks the same q->lock.
                 *
                 * But we need to ensure that set-condition + wakeup after that
                 * can't see us, it should wake up another exclusive waiter if
                 * we fail.
                 */
                list_del_init(&wq_entry->task_list);
                ret = -ERESTARTSYS;
        } else {
                if (list_empty(&wq_entry->task_list)) {
                        if (wq_entry->flags & WQ_FLAG_EXCLUSIVE)
                                __add_wait_queue_entry_tail(q, wq_entry);
                        else
                                __add_wait_queue(q, wq_entry);
                }
                set_current_state(state);
        }
        spin_unlock_irqrestore(&q->lock, flags);

        return ret;
}
EXPORT_SYMBOL(prepare_to_wait_event);

/*
 * Note! These two wait functions are entered with the
 * wait-queue lock held (and interrupts off in the _irq
 * case), so there is no race with testing the wakeup
 * condition in the caller before they add the wait
 * entry to the wake queue.
 */
int do_wait_intr(wait_queue_head_t *wq, wait_queue_entry_t *wait)
{
        if (likely(list_empty(&wait->task_list)))
                __add_wait_queue_entry_tail(wq, wait);

        set_current_state(TASK_INTERRUPTIBLE);
        if (signal_pending(current))
                return -ERESTARTSYS;

        spin_unlock(&wq->lock);
        schedule();
        spin_lock(&wq->lock);
        return 0;
}
EXPORT_SYMBOL(do_wait_intr);

int do_wait_intr_irq(wait_queue_head_t *wq, wait_queue_entry_t *wait)
{
        if (likely(list_empty(&wait->task_list)))
                __add_wait_queue_entry_tail(wq, wait);

        set_current_state(TASK_INTERRUPTIBLE);
        if (signal_pending(current))
                return -ERESTARTSYS;

        spin_unlock_irq(&wq->lock);
        schedule();
        spin_lock_irq(&wq->lock);
        return 0;
}
EXPORT_SYMBOL(do_wait_intr_irq);

/**
 * finish_wait - clean up after waiting in a queue
 * @q: waitqueue waited on
 * @wq_entry: wait descriptor
 *
 * Sets current thread back to running state and removes
 * the wait descriptor from the given waitqueue if still
 * queued.
 */
void finish_wait(wait_queue_head_t *q, struct wait_queue_entry *wq_entry)
{
        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(&wq_entry->task_list)) {
                spin_lock_irqsave(&q->lock, flags);
                list_del_init(&wq_entry->task_list);
                spin_unlock_irqrestore(&q->lock, flags);
        }
}
EXPORT_SYMBOL(finish_wait);

int autoremove_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
{
        int ret = default_wake_function(wq_entry, mode, sync, key);

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

static inline bool is_kthread_should_stop(void)
{
        return (current->flags & PF_KTHREAD) && kthread_should_stop();
}

/*
 * DEFINE_WAIT_FUNC(wait, woken_wake_func);
 *
 * add_wait_queue(&wq, &wait);
 * for (;;) {
 *     if (condition)
 *         break;
 *
 *     p->state = mode;                         condition = true;
 *     smp_mb(); // A                           smp_wmb(); // C
 *     if (!wq_entry->flags & WQ_FLAG_WOKEN)    wq_entry->flags |= WQ_FLAG_WOKEN;
 *         schedule()                           try_to_wake_up();
 *     p->state = TASK_RUNNING;             ~~~~~~~~~~~~~~~~~~
 *     wq_entry->flags &= ~WQ_FLAG_WOKEN;               condition = true;
 *     smp_mb() // B                            smp_wmb(); // C
 *                                              wq_entry->flags |= WQ_FLAG_WOKEN;
 * }
 * remove_wait_queue(&wq, &wait);
 *
 */
long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout)
{
        set_current_state(mode); /* A */
        /*
         * The above implies an smp_mb(), which matches with the smp_wmb() from
         * woken_wake_function() such that if we observe WQ_FLAG_WOKEN we must
         * also observe all state before the wakeup.
         */
        if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
                timeout = schedule_timeout(timeout);
        __set_current_state(TASK_RUNNING);

        /*
         * The below implies an smp_mb(), it too pairs with the smp_wmb() from
         * woken_wake_function() such that we must either observe the wait
         * condition being true _OR_ WQ_FLAG_WOKEN such that we will not miss
         * an event.
         */
        smp_store_mb(wq_entry->flags, wq_entry->flags & ~WQ_FLAG_WOKEN); /* B */

        return timeout;
}
EXPORT_SYMBOL(wait_woken);

int woken_wake_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *key)
{
        /*
         * Although this function is called under waitqueue lock, LOCK
         * doesn't imply write barrier and the users expects write
         * barrier semantics on wakeup functions.  The following
         * smp_wmb() is equivalent to smp_wmb() in try_to_wake_up()
         * and is paired with smp_store_mb() in wait_woken().
         */
        smp_wmb(); /* C */
        wq_entry->flags |= WQ_FLAG_WOKEN;

        return default_wake_function(wq_entry, mode, sync, key);
}
EXPORT_SYMBOL(woken_wake_function);

int wake_bit_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync, void *arg)
{
        struct wait_bit_key *key = arg;
        struct wait_bit_queue *wait_bit
                = container_of(wq_entry, 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(wq_entry, 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,
              wait_bit_action_f *action, 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, mode);
        } 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,
                                    wait_bit_action_f *action, 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 out_of_line_wait_on_bit_timeout(
        void *word, int bit, wait_bit_action_f *action,
        unsigned mode, unsigned long timeout)
{
        wait_queue_head_t *wq = bit_waitqueue(word, bit);
        DEFINE_WAIT_BIT(wait, word, bit);

        wait.key.timeout = jiffies + timeout;
        return __wait_on_bit(wq, &wait, action, mode);
}
EXPORT_SYMBOL_GPL(out_of_line_wait_on_bit_timeout);

int __sched
__wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
                        wait_bit_action_f *action, unsigned mode)
{
        int ret = 0;

        for (;;) {
                prepare_to_wait_exclusive(wq, &q->wait, mode);
                if (test_bit(q->key.bit_nr, q->key.flags)) {
                        ret = action(&q->key, mode);
                        /*
                         * See the comment in prepare_to_wait_event().
                         * finish_wait() does not necessarily takes wq->lock,
                         * but test_and_set_bit() implies mb() which pairs with
                         * smp_mb__after_atomic() before wake_up_page().
                         */
                        if (ret)
                                finish_wait(wq, &q->wait);
                }
                if (!test_and_set_bit(q->key.bit_nr, q->key.flags)) {
                        if (!ret)
                                finish_wait(wq, &q->wait);
                        return 0;
                } else if (ret) {
                        return ret;
                }
        }
}
EXPORT_SYMBOL(__wait_on_bit_lock);

int __sched out_of_line_wait_on_bit_lock(void *word, int bit,
                                         wait_bit_action_f *action, 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);

/**
 * wake_up_bit - wake up a waiter on a bit
 * @word: the word being waited on, a kernel virtual address
 * @bit: the bit of the word being waited on
 *
 * There is a standard hashed waitqueue table for generic use. This
 * is the part of the hashtable's accessor API that wakes up waiters
 * on a bit. For instance, if one were to have waiters on a bitflag,
 * one would call wake_up_bit() after clearing the bit.
 *
 * In order for this to function properly, as it uses waitqueue_active()
 * internally, some kind of memory barrier must be done prior to calling
 * this. Typically, this will be smp_mb__after_atomic(), but in some
 * cases where bitflags are manipulated non-atomically under a lock, one
 * may need to use a less regular barrier, such fs/inode.c's smp_mb(),
 * because spin_unlock() does not guarantee a memory barrier.
 */
void wake_up_bit(void *word, int bit)
{
        __wake_up_bit(bit_waitqueue(word, bit), word, bit);
}
EXPORT_SYMBOL(wake_up_bit);

/*
 * Manipulate the atomic_t address to produce a better bit waitqueue table hash
 * index (we're keying off bit -1, but that would produce a horrible hash
 * value).
 */
static inline wait_queue_head_t *atomic_t_waitqueue(atomic_t *p)
{
        if (BITS_PER_LONG == 64) {
                unsigned long q = (unsigned long)p;
                return bit_waitqueue((void *)(q & ~1), q & 1);
        }
        return bit_waitqueue(p, 0);
}

static int wake_atomic_t_function(struct wait_queue_entry *wq_entry, unsigned mode, int sync,
                                  void *arg)
{
        struct wait_bit_key *key = arg;
        struct wait_bit_queue *wait_bit
                = container_of(wq_entry, struct wait_bit_queue, wait);
        atomic_t *val = key->flags;

        if (wait_bit->key.flags != key->flags ||
            wait_bit->key.bit_nr != key->bit_nr ||
            atomic_read(val) != 0)
                return 0;
        return autoremove_wake_function(wq_entry, mode, sync, key);
}

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

        do {
                prepare_to_wait(wq, &q->wait, mode);
                val = q->key.flags;
                if (atomic_read(val) == 0)
                        break;
                ret = (*action)(val);
        } while (!ret && atomic_read(val) != 0);
        finish_wait(wq, &q->wait);
        return ret;
}

#define DEFINE_WAIT_ATOMIC_T(name, p)                                   \
        struct wait_bit_queue name = {                                  \
                .key = __WAIT_ATOMIC_T_KEY_INITIALIZER(p),              \
                .wait   = {                                             \
                        .private        = current,                      \
                        .func           = wake_atomic_t_function,       \
                        .task_list      =                               \
                                LIST_HEAD_INIT((name).wait.task_list),  \
                },                                                      \
        }

__sched int out_of_line_wait_on_atomic_t(atomic_t *p, int (*action)(atomic_t *),
                                         unsigned mode)
{
        wait_queue_head_t *wq = atomic_t_waitqueue(p);
        DEFINE_WAIT_ATOMIC_T(wait, p);

        return __wait_on_atomic_t(wq, &wait, action, mode);
}
EXPORT_SYMBOL(out_of_line_wait_on_atomic_t);

/**
 * wake_up_atomic_t - Wake up a waiter on a atomic_t
 * @p: The atomic_t being waited on, a kernel virtual address
 *
 * Wake up anyone waiting for the atomic_t to go to zero.
 *
 * Abuse the bit-waker function and its waitqueue hash table set (the atomic_t
 * check is done by the waiter's wake function, not the by the waker itself).
 */
void wake_up_atomic_t(atomic_t *p)
{
        __wake_up_bit(atomic_t_waitqueue(p), p, WAIT_ATOMIC_T_BIT_NR);
}
EXPORT_SYMBOL(wake_up_atomic_t);

__sched int bit_wait(struct wait_bit_key *word, int mode)
{
        schedule();
        if (signal_pending_state(mode, current))
                return -EINTR;
        return 0;
}
EXPORT_SYMBOL(bit_wait);

__sched int bit_wait_io(struct wait_bit_key *word, int mode)
{
        io_schedule();
        if (signal_pending_state(mode, current))
                return -EINTR;
        return 0;
}
EXPORT_SYMBOL(bit_wait_io);

__sched int bit_wait_timeout(struct wait_bit_key *word, int mode)
{
        unsigned long now = READ_ONCE(jiffies);
        if (time_after_eq(now, word->timeout))
                return -EAGAIN;
        schedule_timeout(word->timeout - now);
        if (signal_pending_state(mode, current))
                return -EINTR;
        return 0;
}
EXPORT_SYMBOL_GPL(bit_wait_timeout);

__sched int bit_wait_io_timeout(struct wait_bit_key *word, int mode)
{
        unsigned long now = READ_ONCE(jiffies);
        if (time_after_eq(now, word->timeout))
                return -EAGAIN;
        io_schedule_timeout(word->timeout - now);
        if (signal_pending_state(mode, current))
                return -EINTR;
        return 0;
}
EXPORT_SYMBOL_GPL(bit_wait_io_timeout);