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-rw-r--r--kernel/sched/wait.c35
1 files changed, 25 insertions, 10 deletions
diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
index 2bbba0175ab2..261239392258 100644
--- a/kernel/sched/wait.c
+++ b/kernel/sched/wait.c
@@ -199,24 +199,39 @@ EXPORT_SYMBOL(prepare_to_wait_exclusive);
long prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int state)
{
unsigned long flags;
-
- if (signal_pending_state(state, current))
- return -ERESTARTSYS;
+ long ret = 0;
wait->private = current;
wait->func = autoremove_wake_function;
spin_lock_irqsave(&q->lock, flags);
- if (list_empty(&wait->task_list)) {
- if (wait->flags & WQ_FLAG_EXCLUSIVE)
- __add_wait_queue_tail(q, wait);
- else
- __add_wait_queue(q, wait);
+ 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(&wait->task_list);
+ ret = -ERESTARTSYS;
+ } else {
+ if (list_empty(&wait->task_list)) {
+ if (wait->flags & WQ_FLAG_EXCLUSIVE)
+ __add_wait_queue_tail(q, wait);
+ else
+ __add_wait_queue(q, wait);
+ }
+ set_current_state(state);
}
- set_current_state(state);
spin_unlock_irqrestore(&q->lock, flags);
- return 0;
+ return ret;
}
EXPORT_SYMBOL(prepare_to_wait_event);