Re: [PATCH V3] blk-mq: fix race between complete and BLK_EH_RESET_TIMER

[Jens Axboe <axboe@kernel.dk>]

On 4/12/18 5:59 AM, Ming Lei wrote:
> The normal request completion can be done before or during handling
> BLK_EH_RESET_TIMER, and this race may cause the request to never be
> completed since driver's .timeout() may always return
> BLK_EH_RESET_TIMER.
> 
> This issue can't be fixed completely by driver, since the normal
> completion can be done between returning .timeout() and handling
> BLK_EH_RESET_TIMER.
> 
> This patch fixes the race by introducing rq state of
> MQ_RQ_COMPLETE_IN_RESET, and reading/writing rq's state by holding
> queue lock, which can be per-request actually, but just not necessary
> to introduce one lock for so unusual event.
> 
> Also when .timeout() returns BLK_EH_HANDLED, sync with normal
> completion path before completing this timed-out rq finally for
> avoiding this rq's state touched by normal completion.

I like this approach since it keeps the cost outside of the fast
path. And it's fine to reuse the queue lock for this, instead of
adding a special lock for something we consider a rare occurrence.

>From a quick look this looks sane, but I'll take a closer look
tomrrow and add some testing too.

-- 
Jens Axboe