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-rw-r--r--kernel/sched/wait.c486
1 files changed, 486 insertions, 0 deletions
diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
new file mode 100644
index 0000000000..802d98cf2d
--- /dev/null
+++ b/kernel/sched/wait.c
@@ -0,0 +1,486 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Generic waiting primitives.
+ *
+ * (C) 2004 Nadia Yvette Chambers, Oracle
+ */
+
+void __init_waitqueue_head(struct wait_queue_head *wq_head, const char *name, struct lock_class_key *key)
+{
+ spin_lock_init(&wq_head->lock);
+ lockdep_set_class_and_name(&wq_head->lock, key, name);
+ INIT_LIST_HEAD(&wq_head->head);
+}
+
+EXPORT_SYMBOL(__init_waitqueue_head);
+
+void add_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
+{
+ unsigned long flags;
+
+ wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
+ spin_lock_irqsave(&wq_head->lock, flags);
+ __add_wait_queue(wq_head, wq_entry);
+ spin_unlock_irqrestore(&wq_head->lock, flags);
+}
+EXPORT_SYMBOL(add_wait_queue);
+
+void add_wait_queue_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
+{
+ unsigned long flags;
+
+ wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
+ spin_lock_irqsave(&wq_head->lock, flags);
+ __add_wait_queue_entry_tail(wq_head, wq_entry);
+ spin_unlock_irqrestore(&wq_head->lock, flags);
+}
+EXPORT_SYMBOL(add_wait_queue_exclusive);
+
+void add_wait_queue_priority(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
+{
+ unsigned long flags;
+
+ wq_entry->flags |= WQ_FLAG_EXCLUSIVE | WQ_FLAG_PRIORITY;
+ spin_lock_irqsave(&wq_head->lock, flags);
+ __add_wait_queue(wq_head, wq_entry);
+ spin_unlock_irqrestore(&wq_head->lock, flags);
+}
+EXPORT_SYMBOL_GPL(add_wait_queue_priority);
+
+void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(&wq_head->lock, flags);
+ __remove_wait_queue(wq_head, wq_entry);
+ spin_unlock_irqrestore(&wq_head->lock, flags);
+}
+EXPORT_SYMBOL(remove_wait_queue);
+
+/*
+ * Scan threshold to break wait queue walk.
+ * This allows a waker to take a break from holding the
+ * wait queue lock during the wait queue walk.
+ */
+#define WAITQUEUE_WALK_BREAK_CNT 64
+
+/*
+ * 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 that number of exclusive tasks, and potentially all
+ * the non-exclusive tasks. Normally, exclusive tasks will be at the end of
+ * the list and any non-exclusive tasks will be woken first. A priority task
+ * may be at the head of the list, and can consume the event without any other
+ * tasks being woken.
+ *
+ * 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 int __wake_up_common(struct wait_queue_head *wq_head, unsigned int mode,
+ int nr_exclusive, int wake_flags, void *key,
+ wait_queue_entry_t *bookmark)
+{
+ wait_queue_entry_t *curr, *next;
+ int cnt = 0;
+
+ lockdep_assert_held(&wq_head->lock);
+
+ if (bookmark && (bookmark->flags & WQ_FLAG_BOOKMARK)) {
+ curr = list_next_entry(bookmark, entry);
+
+ list_del(&bookmark->entry);
+ bookmark->flags = 0;
+ } else
+ curr = list_first_entry(&wq_head->head, wait_queue_entry_t, entry);
+
+ if (&curr->entry == &wq_head->head)
+ return nr_exclusive;
+
+ list_for_each_entry_safe_from(curr, next, &wq_head->head, entry) {
+ unsigned flags = curr->flags;
+ int ret;
+
+ if (flags & WQ_FLAG_BOOKMARK)
+ continue;
+
+ ret = curr->func(curr, mode, wake_flags, key);
+ if (ret < 0)
+ break;
+ if (ret && (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
+ break;
+
+ if (bookmark && (++cnt > WAITQUEUE_WALK_BREAK_CNT) &&
+ (&next->entry != &wq_head->head)) {
+ bookmark->flags = WQ_FLAG_BOOKMARK;
+ list_add_tail(&bookmark->entry, &next->entry);
+ break;
+ }
+ }
+
+ return nr_exclusive;
+}
+
+static int __wake_up_common_lock(struct wait_queue_head *wq_head, unsigned int mode,
+ int nr_exclusive, int wake_flags, void *key)
+{
+ unsigned long flags;
+ wait_queue_entry_t bookmark;
+ int remaining = nr_exclusive;
+
+ bookmark.flags = 0;
+ bookmark.private = NULL;
+ bookmark.func = NULL;
+ INIT_LIST_HEAD(&bookmark.entry);
+
+ do {
+ spin_lock_irqsave(&wq_head->lock, flags);
+ remaining = __wake_up_common(wq_head, mode, remaining,
+ wake_flags, key, &bookmark);
+ spin_unlock_irqrestore(&wq_head->lock, flags);
+ } while (bookmark.flags & WQ_FLAG_BOOKMARK);
+
+ return nr_exclusive - remaining;
+}
+
+/**
+ * __wake_up - wake up threads blocked on a waitqueue.
+ * @wq_head: 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
+ *
+ * If this function wakes up a task, it executes a full memory barrier
+ * before accessing the task state. Returns the number of exclusive
+ * tasks that were awaken.
+ */
+int __wake_up(struct wait_queue_head *wq_head, unsigned int mode,
+ int nr_exclusive, void *key)
+{
+ return __wake_up_common_lock(wq_head, mode, nr_exclusive, 0, key);
+}
+EXPORT_SYMBOL(__wake_up);
+
+void __wake_up_on_current_cpu(struct wait_queue_head *wq_head, unsigned int mode, void *key)
+{
+ __wake_up_common_lock(wq_head, mode, 1, WF_CURRENT_CPU, key);
+}
+
+/*
+ * Same as __wake_up but called with the spinlock in wait_queue_head_t held.
+ */
+void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr)
+{
+ __wake_up_common(wq_head, mode, nr, 0, NULL, NULL);
+}
+EXPORT_SYMBOL_GPL(__wake_up_locked);
+
+void __wake_up_locked_key(struct wait_queue_head *wq_head, unsigned int mode, void *key)
+{
+ __wake_up_common(wq_head, mode, 1, 0, key, NULL);
+}
+EXPORT_SYMBOL_GPL(__wake_up_locked_key);
+
+void __wake_up_locked_key_bookmark(struct wait_queue_head *wq_head,
+ unsigned int mode, void *key, wait_queue_entry_t *bookmark)
+{
+ __wake_up_common(wq_head, mode, 1, 0, key, bookmark);
+}
+EXPORT_SYMBOL_GPL(__wake_up_locked_key_bookmark);
+
+/**
+ * __wake_up_sync_key - wake up threads blocked on a waitqueue.
+ * @wq_head: the waitqueue
+ * @mode: which threads
+ * @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.
+ *
+ * If this function wakes up a task, it executes a full memory barrier before
+ * accessing the task state.
+ */
+void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode,
+ void *key)
+{
+ if (unlikely(!wq_head))
+ return;
+
+ __wake_up_common_lock(wq_head, mode, 1, WF_SYNC, key);
+}
+EXPORT_SYMBOL_GPL(__wake_up_sync_key);
+
+/**
+ * __wake_up_locked_sync_key - wake up a thread blocked on a locked waitqueue.
+ * @wq_head: the waitqueue
+ * @mode: which threads
+ * @key: opaque value to be passed to wakeup targets
+ *
+ * The sync wakeup differs in 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.
+ *
+ * If this function wakes up a task, it executes a full memory barrier before
+ * accessing the task state.
+ */
+void __wake_up_locked_sync_key(struct wait_queue_head *wq_head,
+ unsigned int mode, void *key)
+{
+ __wake_up_common(wq_head, mode, 1, WF_SYNC, key, NULL);
+}
+EXPORT_SYMBOL_GPL(__wake_up_locked_sync_key);
+
+/*
+ * __wake_up_sync - see __wake_up_sync_key()
+ */
+void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode)
+{
+ __wake_up_sync_key(wq_head, mode, NULL);
+}
+EXPORT_SYMBOL_GPL(__wake_up_sync); /* For internal use only */
+
+void __wake_up_pollfree(struct wait_queue_head *wq_head)
+{
+ __wake_up(wq_head, TASK_NORMAL, 0, poll_to_key(EPOLLHUP | POLLFREE));
+ /* POLLFREE must have cleared the queue. */
+ WARN_ON_ONCE(waitqueue_active(wq_head));
+}
+
+/*
+ * 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(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
+{
+ unsigned long flags;
+
+ wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
+ spin_lock_irqsave(&wq_head->lock, flags);
+ if (list_empty(&wq_entry->entry))
+ __add_wait_queue(wq_head, wq_entry);
+ set_current_state(state);
+ spin_unlock_irqrestore(&wq_head->lock, flags);
+}
+EXPORT_SYMBOL(prepare_to_wait);
+
+/* Returns true if we are the first waiter in the queue, false otherwise. */
+bool
+prepare_to_wait_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
+{
+ unsigned long flags;
+ bool was_empty = false;
+
+ wq_entry->flags |= WQ_FLAG_EXCLUSIVE;
+ spin_lock_irqsave(&wq_head->lock, flags);
+ if (list_empty(&wq_entry->entry)) {
+ was_empty = list_empty(&wq_head->head);
+ __add_wait_queue_entry_tail(wq_head, wq_entry);
+ }
+ set_current_state(state);
+ spin_unlock_irqrestore(&wq_head->lock, flags);
+ return was_empty;
+}
+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->entry);
+}
+EXPORT_SYMBOL(init_wait_entry);
+
+long prepare_to_wait_event(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry, int state)
+{
+ unsigned long flags;
+ long ret = 0;
+
+ spin_lock_irqsave(&wq_head->lock, flags);
+ if (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 wq_head->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->entry);
+ ret = -ERESTARTSYS;
+ } else {
+ if (list_empty(&wq_entry->entry)) {
+ if (wq_entry->flags & WQ_FLAG_EXCLUSIVE)
+ __add_wait_queue_entry_tail(wq_head, wq_entry);
+ else
+ __add_wait_queue(wq_head, wq_entry);
+ }
+ set_current_state(state);
+ }
+ spin_unlock_irqrestore(&wq_head->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->entry)))
+ __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->entry)))
+ __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
+ * @wq_head: 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(struct wait_queue_head *wq_head, 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->entry)) {
+ spin_lock_irqsave(&wq_head->lock, flags);
+ list_del_init(&wq_entry->entry);
+ spin_unlock_irqrestore(&wq_head->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_careful(&wq_entry->entry);
+
+ return ret;
+}
+EXPORT_SYMBOL(autoremove_wake_function);
+
+/*
+ * DEFINE_WAIT_FUNC(wait, woken_wake_func);
+ *
+ * add_wait_queue(&wq_head, &wait);
+ * for (;;) {
+ * if (condition)
+ * break;
+ *
+ * // in wait_woken() // in woken_wake_function()
+ *
+ * p->state = mode; wq_entry->flags |= WQ_FLAG_WOKEN;
+ * smp_mb(); // A try_to_wake_up():
+ * if (!(wq_entry->flags & WQ_FLAG_WOKEN)) <full barrier>
+ * schedule() if (p->state & mode)
+ * p->state = TASK_RUNNING; p->state = TASK_RUNNING;
+ * wq_entry->flags &= ~WQ_FLAG_WOKEN; ~~~~~~~~~~~~~~~~~~
+ * smp_mb(); // B condition = true;
+ * } smp_mb(); // C
+ * remove_wait_queue(&wq_head, &wait); wq_entry->flags |= WQ_FLAG_WOKEN;
+ */
+long wait_woken(struct wait_queue_entry *wq_entry, unsigned mode, long timeout)
+{
+ /*
+ * The below executes an smp_mb(), which matches with the full barrier
+ * executed by the try_to_wake_up() in woken_wake_function() such that
+ * either we see the store to wq_entry->flags in woken_wake_function()
+ * or woken_wake_function() sees our store to current->state.
+ */
+ set_current_state(mode); /* A */
+ if (!(wq_entry->flags & WQ_FLAG_WOKEN) && !kthread_should_stop_or_park())
+ timeout = schedule_timeout(timeout);
+ __set_current_state(TASK_RUNNING);
+
+ /*
+ * The below executes an smp_mb(), which matches with the smp_mb() (C)
+ * in woken_wake_function() such that either we see the wait condition
+ * being true or the store to wq_entry->flags in woken_wake_function()
+ * follows ours in the coherence order.
+ */
+ 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)
+{
+ /* Pairs with the smp_store_mb() in wait_woken(). */
+ smp_mb(); /* C */
+ wq_entry->flags |= WQ_FLAG_WOKEN;
+
+ return default_wake_function(wq_entry, mode, sync, key);
+}
+EXPORT_SYMBOL(woken_wake_function);