block: check for timeout function in blk_rq_timed_out()

rq_timed_out_fn might have been unset while the request
was in flight, so we need to check for it in blk_rq_timed_out().

Acked-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Stefan Weinhuber <wein@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

block/blk-timeout.c

@@ -82,8 +82,9 @@ void blk_delete_timer(struct request *req)
 static void blk_rq_timed_out(struct request *req)
 {
 	struct request_queue *q = req->q;
-	enum blk_eh_timer_return ret;
+	enum blk_eh_timer_return ret = BLK_EH_RESET_TIMER;
 
+	if (q->rq_timed_out_fn)
 		ret = q->rq_timed_out_fn(req);
 	switch (ret) {
 	case BLK_EH_HANDLED: