linux-kernel - [PATCH AUTOSEL 5.14 05/34] blk-mq: avoid to iterate over stale request

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Date:   Wed, 22 Sep 2021 23:37:53 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Ming Lei <ming.lei@...hat.com>, linux-scsi@...r.kernel.org,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        luojiaxing <luojiaxing@...wei.com>, Jens Axboe <axboe@...nel.dk>,
        Sasha Levin <sashal@...nel.org>, linux-block@...r.kernel.org
Subject: [PATCH AUTOSEL 5.14 05/34] blk-mq: avoid to iterate over stale request

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

[ Upstream commit 67f3b2f822b7e71cfc9b42dbd9f3144fa2933e0b ]

blk-mq can't run allocating driver tag and updating ->rqs[tag]
atomically, meantime blk-mq doesn't clear ->rqs[tag] after the driver
tag is released.

So there is chance to iterating over one stale request just after the
tag is allocated and before updating ->rqs[tag].

scsi_host_busy_iter() calls scsi_host_check_in_flight() to count scsi
in-flight requests after scsi host is blocked, so no new scsi command can
be marked as SCMD_STATE_INFLIGHT. However, driver tag allocation still can
be run by blk-mq core. One request is marked as SCMD_STATE_INFLIGHT,
but this request may have been kept in another slot of ->rqs[], meantime
the slot can be allocated out but ->rqs[] isn't updated yet. Then this
in-flight request is counted twice as SCMD_STATE_INFLIGHT. This way causes
trouble in handling scsi error.

Fixes the issue by not iterating over stale request.

Cc: linux-scsi@...r.kernel.org
Cc: "Martin K. Petersen" <martin.petersen@...cle.com>
Reported-by: luojiaxing <luojiaxing@...wei.com>
Signed-off-by: Ming Lei <ming.lei@...hat.com>
Link: https://lore.kernel.org/r/20210906065003.439019-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 block/blk-mq-tag.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 86f87346232a..ff5caeb82542 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -208,7 +208,7 @@ static struct request *blk_mq_find_and_get_req(struct blk_mq_tags *tags,

 	spin_lock_irqsave(&tags->lock, flags);
 	rq = tags->rqs[bitnr];
-	if (!rq || !refcount_inc_not_zero(&rq->ref))
+	if (!rq || rq->tag != bitnr || !refcount_inc_not_zero(&rq->ref))
 		rq = NULL;
 	spin_unlock_irqrestore(&tags->lock, flags);
 	return rq;
-- 
2.30.2