Re: [PATCH v3 3/5] nvme-fabrics: avoid double request completion for nvmf_fail_nonready_command

From: Hannes Reinecke <hare@suse.de>
To: Chao Leng <lengchao@huawei.com>, linux-nvme@lists.infradead.org
Cc: axboe@kernel.dk, linux-block@vger.kernel.org, sagi@grimberg.me,
	axboe@fb.com, kbusch@kernel.org, hch@lst.de
Subject: Re: [PATCH v3 3/5] nvme-fabrics: avoid double request completion for nvmf_fail_nonready_command
Date: Thu, 21 Jan 2021 09:58:37 +0100	[thread overview]
Message-ID: <fda1fdb8-8a9d-2e95-4d08-8d8ee1df450d@suse.de> (raw)
In-Reply-To: <20210121070330.19701-4-lengchao@huawei.com>

On 1/21/21 8:03 AM, Chao Leng wrote:
> When reconnect, the request may be completed with NVME_SC_HOST_PATH_ERROR
> in nvmf_fail_nonready_command. The state of request will be changed to
> MQ_RQ_IN_FLIGHT before call nvme_complete_rq. If free the request
> asynchronously such as in nvme_submit_user_cmd, in extreme scenario
> the request may be completed again in tear down process.
> nvmf_fail_nonready_command do not need calling blk_mq_start_request
> before complete the request. nvmf_fail_nonready_command should set
> the state of request to MQ_RQ_COMPLETE before complete the request.
> 

So what you are saying is that there is a race condition between
blk_mq_start_request()
and
nvme_complete_request()

> Signed-off-by: Chao Leng <lengchao@huawei.com>
> ---
>   drivers/nvme/host/fabrics.c | 4 +---
>   1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/nvme/host/fabrics.c b/drivers/nvme/host/fabrics.c
> index 72ac00173500..874e4320e214 100644
> --- a/drivers/nvme/host/fabrics.c
> +++ b/drivers/nvme/host/fabrics.c
> @@ -553,9 +553,7 @@ blk_status_t nvmf_fail_nonready_command(struct nvme_ctrl *ctrl,
>   	    !blk_noretry_request(rq) && !(rq->cmd_flags & REQ_NVME_MPATH))
>   		return BLK_STS_RESOURCE;
>   
> -	nvme_req(rq)->status = NVME_SC_HOST_PATH_ERROR;
> -	blk_mq_start_request(rq);
> -	nvme_complete_rq(rq);
> +	nvme_complete_failed_req(rq);
>   	return BLK_STS_OK;
>   }
>   EXPORT_SYMBOL_GPL(nvmf_fail_nonready_command);
> I'd rather have 'nvme_complete_failed_req()' accept the status as 
argument, like

nvme_complete_failed_request(rq, NVME_SC_HOST_PATH_ERROR)

that way it's obvious what is happening, and the status isn't hidden in 
the function.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
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