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

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Message-ID: <CACVXFVPcuqzXiKUnaFxhw4CuqGpFdkmvfw=7yJAydXTYLKXDCw@mail.gmail.com>
Date:   Fri, 15 Jun 2018 10:49:29 +0800
From:   Ming Lei <tom.leiming@...il.com>
To:     "jianchao.wang" <jianchao.w.wang@...cle.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

On Fri, Jun 15, 2018 at 10:22 AM, jianchao.wang
<jianchao.w.wang@...cle.com> wrote:
> Hi Ming
>
> On 06/15/2018 10:17 AM, Ming Lei wrote:
>> On Fri, Jun 15, 2018 at 9:57 AM, Jianchao Wang
>> <jianchao.w.wang@...cle.com> wrote:
>>> After f6e7d48 (block: remove BLK_EH_HANDLED), LLDD is responsible
>>> to complete the timed out request, however, for blk-legacy, the
>>> 'complete' is still marked, blk_complete_request will do nothing,
>>> we export __blk_complete_request for LLDD to complete the request
>>> in timeout path.
>>>
>>> Signed-off-by: Jianchao Wang <jianchao.w.wang@...cle.com>
>>> ---
>>>  block/blk-softirq.c | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/block/blk-softirq.c b/block/blk-softirq.c
>>> index 01e2b35..15c1f5e 100644
>>> --- a/block/blk-softirq.c
>>> +++ b/block/blk-softirq.c
>>> @@ -144,6 +144,7 @@ void __blk_complete_request(struct request *req)
>>>
>>>         local_irq_restore(flags);
>>>  }
>>> +EXPORT_SYMBOL(__blk_complete_request);
>>>
>>>  /**
>>>   * blk_complete_request - end I/O on a request
>>> --
>>> 2.7.4
>>>
>>
>> Looks non-blk-mq timeout code need to convert to ref-counter
>> based approach too?
>
> IMO, ref-counter is just to fix the blk-mq req life recycle issue.

Just thought of that, it is one blk-mq specific issue.

> It cannot replace the blk_mark_rq_complete which could avoid the race between
> timeout and io completion path.
> Or maybe my understanding is wrong ...

I didn't mean that this patch is unnecessary.

But the question is that given driver has to deal with race between timeout
and normal completion, why don't you follow blk-mq's way to move
the atomic state change into __blk_complete_request()?


Thanks,
Ming Lei