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Subject: Re: [PATCH 1/2] block: export __blk_complete_request
To:     Ming Lei <tom.leiming@gmail.com>
Cc:     Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@lst.de>,
        James Bottomley <jejb@linux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        linux-block <linux-block@vger.kernel.org>,
        Linux SCSI List <linux-scsi@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
References: <1529027847-29085-1-git-send-email-jianchao.w.wang@oracle.com>
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 <3dd3f82a-5b68-f039-3a8a-7c5fe4e24c3e@oracle.com>
From:   "jianchao.wang" <jianchao.w.wang@oracle.com>
Message-ID: <e5344293-b0b7-d2e0-f2e7-c0700efdfbe4@oracle.com>
Date:   Fri, 15 Jun 2018 10:44:38 +0800
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On 06/15/2018 10:22 AM, jianchao.wang 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@oracle.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@oracle.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.
> 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 ? 

> Or maybe my understanding is wrong ...
> 
> Thanks
> Jianchao
>>
>