linux-kernel - [PATCH 5.7 160/166] blk-mq: consider non-idle request as "inflight" in blk_mq_rq

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Date:   Tue, 14 Jul 2020 20:45:25 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ming Lei <ming.lei@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>, Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 5.7 160/166] blk-mq: consider non-idle request as "inflight" in blk_mq_rq_inflight()

From: Ming Lei <ming.lei@...hat.com>

commit 05a4fed69ff00a8bd83538684cb602a4636b07a7 upstream.

dm-multipath is the only user of blk_mq_queue_inflight().  When
dm-multipath calls blk_mq_queue_inflight() to check if it has
outstanding IO it can get a false negative.  The reason for this is
blk_mq_rq_inflight() doesn't consider requests that are no longer
MQ_RQ_IN_FLIGHT but that are now MQ_RQ_COMPLETE (->complete isn't
called or finished yet) as "inflight".

This causes request-based dm-multipath's dm_wait_for_completion() to
return before all outstanding dm-multipath requests have actually
completed.  This breaks DM multipath's suspend functionality because
blk-mq requests complete after DM's suspend has finished -- which
shouldn't happen.

Fix this by considering any request not in the MQ_RQ_IDLE state
(so either MQ_RQ_COMPLETE or MQ_RQ_IN_FLIGHT) as "inflight" in
blk_mq_rq_inflight().

Fixes: 3c94d83cb3526 ("blk-mq: change blk_mq_queue_busy() to blk_mq_queue_inflight()")
Signed-off-by: Ming Lei <ming.lei@...hat.com>
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
Cc: stable@...r.kernel.org
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 block/blk-mq.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -803,10 +803,10 @@ static bool blk_mq_rq_inflight(struct bl
 			       void *priv, bool reserved)
 {
 	/*
-	 * If we find a request that is inflight and the queue matches,
+	 * If we find a request that isn't idle and the queue matches,
 	 * we know the queue is busy. Return false to stop the iteration.
 	 */
-	if (rq->state == MQ_RQ_IN_FLIGHT && rq->q == hctx->queue) {
+	if (blk_mq_request_started(rq) && rq->q == hctx->queue) {
 		bool *busy = priv;

 		*busy = true;