linux-kernel - Re: [PATCH 5/5] nvme: use __blk_mq_complete

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Date:   Sun, 24 Jun 2018 21:07:50 +0300
From:   Sagi Grimberg <sagi@...mberg.me>
To:     "jianchao.wang" <jianchao.w.wang@...cle.com>,
        Christoph Hellwig <hch@....de>
Cc:     axboe@...nel.dk, martin.petersen@...cle.com, keith.busch@...el.com,
        josef@...icpanda.com, ulf.hansson@...aro.org,
        linux-block@...r.kernel.org, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] nvme: use __blk_mq_complete_request in timeout path


> Hi Christoph
> 
> Thanks for your kindly response.
> 
> On 06/20/2018 10:39 PM, Christoph Hellwig wrote:
>>> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
>>> index 73a97fc..2a161f6 100644
>>> --- a/drivers/nvme/host/pci.c
>>> +++ b/drivers/nvme/host/pci.c
>>> @@ -1203,6 +1203,7 @@ static enum blk_eh_timer_return nvme_timeout(struct request *req, bool reserved)
>>>   		nvme_warn_reset(dev, csts);
>>>   		nvme_dev_disable(dev, false);
>>>   		nvme_reset_ctrl(&dev->ctrl);
>>> +		__blk_mq_complete_request(req);
>>>   		return BLK_EH_DONE;
>>>   	}
>>>   
>>> @@ -1213,6 +1214,11 @@ static enum blk_eh_timer_return nvme_timeout(struct request *req, bool reserved)
>>>   		dev_warn(dev->ctrl.device,
>>>   			 "I/O %d QID %d timeout, completion polled\n",
>>>   			 req->tag, nvmeq->qid);
>>> +		/*
>>> +		 * nvme_end_request will invoke blk_mq_complete_request,
>>> +		 * it will do nothing for this timed out request.
>>> +		 */
>>> +		__blk_mq_complete_request(req);
>>
>> And this clearly is bogus.  We want to iterate over the tagetset
>> and cancel all requests, not do that manually here.
>>
>> That was the whole point of the original change.
>>
> 
> For nvme-pci, we indeed have an issue that when nvme_reset_work->nvme_dev_disable returns, timeout path maybe still
> running and the nvme_dev_disable invoked by timeout path will race with the nvme_reset_work.
> However, the hole is still there right now w/o my changes, but just narrower.

Given the amount of fixes (and fixes of fixes) we had in the timeout 
handler, maybe it'd be a good idea to step back and take a another look?

Won't it be better to avoid disabling the device and return
BLK_EH_RESET_TIMER if we are not aborting in the timeout handler?