Re: [PATCH v2] blk-mq: Fix race between resetting the timer and completion handling

["tj@kernel.org" <tj@kernel.org>]

Hello,

On Wed, Feb 07, 2018 at 07:03:56PM +0000, Bart Van Assche wrote:
> I tried the above patch but already during the first iteration of the test I
> noticed that the test hung, probably due to the following request that got stuck:
> 
> $ (cd /sys/kernel/debug/block && grep -aH . */*/*/rq_list)
> 00000000a98cff60 {.op=SCSI_IN, .cmd_flags=, .rq_flags=MQ_INFLIGHT|PREEMPT|QUIET|IO_STAT|PM,
>  .state=idle, .tag=22, .internal_tag=-1, .cmd=Synchronize Cache(10) 35 00 00 00 00 00, .retries=0,
>  .result = 0x0, .flags=TAGGED, .timeout=60.000, allocated 872.690 s ago}

I'm wonder how this happened, so we can lose a completion when it
races against BLK_EH_RESET_TIMER; however, the command should timeout
later cuz the timer is running again now.  Maybe we actually had the
memory barrier race that you pointed out in the other message?

Thanks.

-- 
tejun