blk-mq: do not do head insertions post-pre-flush commands

blk_flush_complete_seq currently queues requests that write data after
a pre-flush from the flush state machine at the head of the queue.
This doesn't really make sense, as the original request bypassed all
queue lists by directly diverting to blk_insert_flush from
blk_mq_submit_bio.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://lore.kernel.org/r/20230519044050.107790-7-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-flush.c

@@ -188,7 +188,7 @@ static void blk_flush_complete_seq(struct request *rq,
 
 	case REQ_FSEQ_DATA:
 		list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
-		blk_mq_add_to_requeue_list(rq, BLK_MQ_INSERT_AT_HEAD);
+		blk_mq_add_to_requeue_list(rq, 0);
 		blk_mq_kick_requeue_list(q);
 		break;