blk-mq: don't issue request directly in case that current is to be blocked

When flushing plug list in case that current will be blocked, we can't
issue request directly because ->queue_rq() may sleep, otherwise scheduler
may complain.

Fixes: dc5fc361d8 ("block: attempt direct issue of plug list")
Signed-off-by: Ming Lei <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

block/blk-mq.c

@@ -2223,7 +2223,7 @@ void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
 		return;
 	plug->rq_count = 0;
 
-	if (!plug->multiple_queues && !plug->has_elevator) {
+	if (!plug->multiple_queues && !plug->has_elevator && !from_schedule) {
 		blk_mq_plug_issue_direct(plug, from_schedule);
 		if (rq_list_empty(plug->mq_list))
 			return;