linux-kernel - Re: [PATCH V3 5/7] ublk_drv: consider recovery feature in aborting mechanism

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Date:   Tue, 20 Sep 2022 13:03:04 +0800
From:   Ziyang Zhang <ZiyangZhang@...ux.alibaba.com>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     axboe@...nel.dk, xiaoguang.wang@...ux.alibaba.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        joseph.qi@...ux.alibaba.com
Subject: Re: [PATCH V3 5/7] ublk_drv: consider recovery feature in aborting
 mechanism

On 2022/9/20 12:49, Ming Lei wrote:
> On Tue, Sep 20, 2022 at 12:39:31PM +0800, Ziyang Zhang wrote:
>> On 2022/9/20 12:01, Ming Lei wrote:
>>> On Tue, Sep 20, 2022 at 11:24:12AM +0800, Ziyang Zhang wrote:
>>>> On 2022/9/20 11:04, Ming Lei wrote:
>>>>> On Tue, Sep 20, 2022 at 09:49:33AM +0800, Ziyang Zhang wrote:
>>>>>
>>>>> Follows the delta patch against patch 5 for showing the idea:
>>>>>
>>>>>
>>>>> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
>>>>> index 4409a130d0b6..60c5786c4711 100644
>>>>> --- a/drivers/block/ublk_drv.c
>>>>> +++ b/drivers/block/ublk_drv.c
>>>>> @@ -656,7 +656,8 @@ static void ublk_complete_rq(struct request *req)
>>>>>   * Also aborting may not be started yet, keep in mind that one failed
>>>>>   * request may be issued by block layer again.
>>>>>   */
>>>>> -static void __ublk_fail_req(struct ublk_io *io, struct request *req)
>>>>> +static void __ublk_fail_req(struct ublk_queue *ubq, struct ublk_io *io,
>>>>> +		struct request *req)
>>>>>  {
>>>>>  	WARN_ON_ONCE(io->flags & UBLK_IO_FLAG_ACTIVE);
>>>>>  
>>>>> @@ -667,7 +668,10 @@ static void __ublk_fail_req(struct ublk_io *io, struct request *req)
>>>>>  				req->tag,
>>>>>  				io->flags);
>>>>>  		io->flags |= UBLK_IO_FLAG_ABORTED;
>>>>> -		blk_mq_end_request(req, BLK_STS_IOERR);
>>>>> +		if (ublk_queue_can_use_recovery_reissue(ubq))
>>>>> +			blk_mq_requeue_request(req, false);
>>>>
>>>> Here is one problem:
>>>> We reset io->flags to 0 in ublk_queue_reinit() and it is called before new
>>>
>>> As we agreed, ublk_queue_reinit() will be moved to ublk_ch_release(), when there isn't
>>> any inflight request, which is completed by either ublk server or __ublk_fail_req().
>>>
>>> So clearing io->flags isn't related with quisceing device.
>>>
>>>> ubq_daemon with FETCH_REQ is accepted. ublk_abort_queue() is not protected with
>>>> ub_mutex and it is called many times in monitor_work. So same rq may be requeued
>>>> multiple times.
>>>
>>> UBLK_IO_FLAG_ABORTED is set for the slot, so one req is only ended or
>>> requeued just once.
>>
>> Yes, we can move ublk_queue_reinit() into ublk_ch_release(), but monitor_work is scheduled
>> periodically so ublk_abort_queue() is called multiple times. As ublk_queue_reinit() clear
>> io->flags, ublk_abort_queue() can requeue the same rq twice. Note that monitor_work can be
>> scheduled after ublk_ch_release().
> 
> No, monitor work is supposed to be shutdown after in-flight requests are
> drained.


Let's add cancel_delayed_work_sync(&ub->monitor_work) in ublk_ch_release().
monitor_work should not be scheduled after ub's state is QUIESCED.

Regards,
Zhang.