[PATCH] block: re-introduce blk_mq_complete_request_sync

[Sagi Grimberg]

>>> This may just reduce the probability. The concurrency of timeout and 
>>> teardown will cause the same request
>>> be treated repeatly, this is not we expected.
>>
>> That is right, not like SCSI, NVME doesn't apply atomic request 
>> completion, so
>> request may be completed/freed from both timeout & nvme_cancel_request().
>>
>> .teardown_lock still may cover the race with Sagi's patch because 
>> teardown
>> actually cancels requests in sync style.
> In extreme scenarios, the request may be already retry success(rq state 
> change to inflight).
> Timeout processing may wrongly stop the queue and abort the request.
> teardown_lock serialize the process of timeout and teardown, but do not 
> avoid the race.
> It might not be safe.

Not sure I understand the scenario you are describing.

what do you mean by "In extreme scenarios, the request may be already 
retry success(rq state change to inflight)"?

What will retry the request? only when the host will reconnect
the request will be retried.

We can call nvme_sync_queues in the last part of the teardown, but
I still don't understand the race here.