--- y/kernel/watch_queue.c
+++ w/kernel/watch_queue.c
@@ -83,10 +83,10 @@ static bool post_one_notification(struct
 	if (!pipe)
 		return false;
 
-	spin_lock_irq(&pipe->rd_wait.lock);
-
+	spin_lock_bh(&wqueue->lock);
 	if (wqueue->defunct)
-		goto out;
+		goto unlock;
+	spin_lock_irq(&pipe->rd_wait.lock);
 
 	mask = pipe->ring_size - 1;
 	head = pipe->head;
@@ -126,6 +126,8 @@ out:
 	spin_unlock_irq(&pipe->rd_wait.lock);
 	if (done)
 		kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
+unlock:
+	spin_unlock_bh(&wqueue->lock);
 	return done;
 
 lost: