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@xxxxxxxxxxxxxxx Cc: "Martin K. Petersen" <martin.petersen@xxxxxxxxxx> Reported-by: luojiaxing <luojiaxing@xxxxxxxxxx> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx> --- 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; -- 2.31.1
