[PATCH] missing lock in get_request_wait()

We must grab lock before checking rl->count.

drivers/block/ll_rw_blk.c

@@ -1358,11 +1358,19 @@ static struct request *get_request_wait(request_queue_t *q, int rw)
 
 	generic_unplug_device(q);
 	do {
+		int block = 0;
+
 		prepare_to_wait_exclusive(&rl->wait, &wait,
 					TASK_UNINTERRUPTIBLE);
+		spin_lock_irq(q->queue_lock);
 		if (!rl->count)
+			block = 1;
+		spin_unlock_irq(q->queue_lock);
+
+		if (block)
 			io_schedule();
 		finish_wait(&rl->wait, &wait);
+
 		spin_lock_irq(q->queue_lock);
 		rq = get_request(q, rw);
 		spin_unlock_irq(q->queue_lock);