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Date:   Wed, 22 Sep 2021 23:38:18 -0400
From:   Sasha Levin <>
Cc:     Ming Lei <>,,
        "Martin K. Petersen" <>,
        luojiaxing <>, Jens Axboe <>,
        Sasha Levin <>,
Subject: [PATCH AUTOSEL 5.10 05/26] blk-mq: avoid to iterate over stale request

From: Ming Lei <>

[ 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: "Martin K. Petersen" <>
Reported-by: luojiaxing <>
Signed-off-by: Ming Lei <>
Signed-off-by: Jens Axboe <>
Signed-off-by: Sasha Levin <>
 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 c4f2f6c123ae..16ad9e656610 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -207,7 +207,7 @@ 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;

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