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

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Date:   Thu, 21 Jun 2018 10:09:20 +0800
From:   "jianchao.wang" <jianchao.w.wang@...cle.com>
To:     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. 

Thanks
Jianchao