Btrfs: convert nested spin_lock_irqsave to spin_lock

If spin_lock_irqsave is called twice in a row with the same second
argument, the interrupt state at the point of the second call overwrites
the value saved by the first call.  Indeed, the second call does not need
to save the interrupt state, so it is changed to a simple spin_lock.
Signed-off-by: NJulia Lawall <julia@diku.dk>
Signed-off-by: NChris Mason <chris.mason@oracle.com>

fs/btrfs/async-thread.c

@@ -424,11 +424,11 @@ int btrfs_requeue_work(struct btrfs_work *work)
 	 * list
 	 */
 	if (worker->idle) {
-		spin_lock_irqsave(&worker->workers->lock, flags);
+		spin_lock(&worker->workers->lock);
 		worker->idle = 0;
 		list_move_tail(&worker->worker_list,
 			       &worker->workers->worker_list);
-		spin_unlock_irqrestore(&worker->workers->lock, flags);
+		spin_unlock(&worker->workers->lock);
 	}
 	if (!worker->working) {
 		wake = 1;