Hi Jianchao,

Jianchao Wang - 17.04.18, 05:46:

rq->gstate and rq->aborted_gstate both are zero before rqs are allocated. If we have a small timeout, when the timer fires, there could be rqs that are never allocated, and also there could be rq that has been allocated but not initialized and started. At the moment, the rq->gstate and rq->aborted_gstate both are 0, thus the blk_mq_terminate_expired will identify the rq is timed out and invoke .timeout early.

For testing it I add it to 4.16.2 with the patches I have already?

- '[PATCH] blk-mq_Directly schedule q->timeout_work when aborting a request.mbox'

- '[PATCH v2] block: Change a rcu_read_{lock,unlock}_sched() pair into rcu_read_{lock,unlock}().mbox'

- '[PATCH V4 1_2] blk-mq_set RQF_MQ_TIMEOUT_EXPIRED when the rq'''s timeout isn'''t handled.mbox'

- '[PATCH V4 2_2] blk-mq_fix race between complete and BLK_EH_RESET_TIMER.mbox'

For scsi, this will cause scsi_times_out to be invoked before the scsi_cmnd is not initialized, scsi_cmnd->device is still NULL at the moment, then we will get crash.

Cc: Bart Van Assche bart.vanassche@wdc.com Cc: Tejun Heo tj@kernel.org Cc: Ming Lei ming.lei@redhat.com Cc: Martin Steigerwald Martin@Lichtvoll.de Cc: stable@vger.kernel.org Signed-off-by: Jianchao Wang jianchao.w.wang@oracle.com

---

block/blk-core.c | 4 ++++ block/blk-mq.c | 7 +++++++ 2 files changed, 11 insertions(+)

diff --git a/block/blk-core.c b/block/blk-core.c index abcb868..ce62681 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -201,6 +201,10 @@ void blk_rq_init(struct request_queue *q, struct request *rq) rq->part = NULL; seqcount_init(&rq->gstate_seq); u64_stats_init(&rq->aborted_gstate_sync);

• /*

• * See comment of blk_mq_init_request
  

• */
  

• WRITE_ONCE(rq->gstate, MQ_RQ_GEN_INC);

} EXPORT_SYMBOL(blk_rq_init);

diff --git a/block/blk-mq.c b/block/blk-mq.c index f5c7dbc..d62030a 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2069,6 +2069,13 @@ static int blk_mq_init_request(struct blk_mq_tag_set *set, struct request *rq,

seqcount_init(&rq->gstate_seq); u64_stats_init(&rq->aborted_gstate_sync);

• /*

• * start gstate with gen 1 instead of 0, otherwise it will be equal
  

• * to aborted_gstate, and be identified timed out by
  

• * blk_mq_terminate_expired.
  

• */
  

• WRITE_ONCE(rq->gstate, MQ_RQ_GEN_INC);
• return 0;

}