linux-kernel - Re: [PATCH 1/2] block: export __blk_complete

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Date:   Fri, 15 Jun 2018 11:26:03 +0800
From:   "jianchao.wang" <jianchao.w.wang@...cle.com>
To:     Ming Lei <tom.leiming@...il.com>
Cc:     Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
        James Bottomley <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-block <linux-block@...r.kernel.org>,
        Linux SCSI List <linux-scsi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] block: export __blk_complete_request

Hi Ming

On 06/15/2018 11:20 AM, Ming Lei wrote:
> On Fri, Jun 15, 2018 at 11:04 AM, jianchao.wang
> <jianchao.w.wang@...cle.com> wrote:
>> Hi Ming
>>
>> Thanks for your kindly response.
>>
>> On 06/15/2018 10:56 AM, Ming Lei wrote:
>>>>> IMO, ref-counter is just to fix the blk-mq req life recycle issue.
>>>>> It cannot replace the blk_mark_rq_complete which could avoid the race between
>>>>> timeout and io completion path.
>>>> The .timeout return BLK_EH_DONE doesn't always mean the request has been completed.
>>>> Such as scsi-mid layer, its .timeout callback return BLK_EH_DONE but the timed out
>>>> request is still in abort or eh process. What if a completion irq come during that ?
>>> For blk-mq, it is avoided by the atomic state change in
>>> __blk_mq_complete_request(),
>>> that is why I mentioned the question in my last reply.
>>>
>>
>> but blk_mq_check_expired doesn't do that.
>> do I miss anything ?
> 
> Right, that is the difference between blk-mq and legacy now, 

Sorry, I cannot follow your point.
blk_mq_check_expired doesn't do a atmoc state change from IN-FLIGHT to COMPLETE.
__blk_mq_complete_request could still proceed to complete a timed out request
which is in scsi abort or eh process. Is it really OK ?


Thanks
Jianchao


> then if scsi-mq
> drivers can work well, they should work well with the following change in the
> non-mq mode:
> 
> diff --git a/block/blk-timeout.c b/block/blk-timeout.c
> index 4b8a48d48ba1..9fce09d55652 100644
> --- a/block/blk-timeout.c
> +++ b/block/blk-timeout.c
> @@ -88,7 +88,6 @@ static void blk_rq_timed_out(struct request *req)
>         switch (ret) {
>         case BLK_EH_RESET_TIMER:
>                 blk_add_timer(req);
> -               blk_clear_rq_complete(req);
>                 break;
>         case BLK_EH_DONE:
>                 /*
> @@ -115,8 +114,7 @@ static void blk_rq_check_expired(struct request
> *rq, unsigned long *next_timeout
>                 /*
>                  * Check if we raced with end io completion
>                  */
> -               if (!blk_mark_rq_complete(rq))
> -                       blk_rq_timed_out(rq);
> +               blk_rq_timed_out(rq);
>         } else if (!*next_set || time_after(*next_timeout, deadline)) {
>                 *next_timeout = deadline;
>                 *next_set = 1;
> 
> 
> Thanks,
> Ming Lei
>