Re: [PATCH 1/2] nvme: pci: simplify timeout handling

Ming Lei
2018-04-28T22:27:33Z

On Sun, Apr 29, 2018 at 5:57 AM, Ming Lei <tom.leiming@gmail.com> wrote:
> On Sat, Apr 28, 2018 at 10:00 PM, jianchao.wang
> <jianchao.w.wang@oracle.com> wrote:
>> Hi ming
>>
>> On 04/27/2018 10:57 PM, Ming Lei wrote:
>>> I may not understand your point, once blk_sync_queue() returns, the
>>> timer itself is deactivated, meantime the synced .nvme_timeout() only
>>> returns EH_NOT_HANDLED before the deactivation.
>>>
>>> That means this timer won't be expired any more, so could you explain
>>> a bit why timeout can come again after blk_sync_queue() returns
>>
>> Please consider the following case:
>>
>> blk_sync_queue
>> -> del_timer_sync
>> blk_mq_timeout_work
>> -> blk_mq_check_expired // return the timeout value
>> -> blk_mq_terninate_expired
>> -> .timeout //return EH_NOT_HANDLED
>> -> mod_timer // setup the timer again based on the result of blk_mq_check_expired
>> -> cancel_work_sync
>> So after the blk_sync_queue, the timer may come back again, then the timeout work.
>
> OK, I was trying to avoid to use blk_abort_request(), but looks we
> may have to depend on it or similar way.
>
> BTW, that means blk_sync_queue() has been broken, even though the uses
> in blk_cleanup_queue().
>
> Another approach is to introduce one perpcu_ref of
> 'q->timeout_usage_counter' for
> syncing timeout, seems a bit over-kill too, but simpler in both theory
> and implement.

Or one timout_mutex is enough.

Thanks,
Ming Lei