linux-kernel - Re: [PATCH v7 4/6] nbd: don't start request if nbd_queue

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Date:   Thu, 16 Sep 2021 15:58:10 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Yu Kuai <yukuai3@...wei.com>
Cc:     josef@...icpanda.com, axboe@...nel.dk, hch@...radead.org,
        linux-block@...r.kernel.org, nbd@...er.debian.org,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com
Subject: Re: [PATCH v7 4/6] nbd: don't start request if nbd_queue_rq() failed

On Wed, Sep 15, 2021 at 05:20:08PM +0800, Yu Kuai wrote:
> Currently, blk_mq_end_request() will be called if nbd_queue_rq()
> failed, thus start request in such situation is useless.
> 
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> Reviewed-by: Christoph Hellwig <hch@....de>
> ---
>  drivers/block/nbd.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index c724a5bd7fa4..22c91d8901f6 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -934,7 +934,6 @@ static int nbd_handle_cmd(struct nbd_cmd *cmd, int index)
>  	if (!refcount_inc_not_zero(&nbd->config_refs)) {
>  		dev_err_ratelimited(disk_to_dev(nbd->disk),
>  				    "Socks array is empty\n");
> -		blk_mq_start_request(req);
>  		return -EINVAL;
>  	}
>  	config = nbd->config;
> @@ -943,7 +942,6 @@ static int nbd_handle_cmd(struct nbd_cmd *cmd, int index)
>  		dev_err_ratelimited(disk_to_dev(nbd->disk),
>  				    "Attempted send on invalid socket\n");
>  		nbd_config_put(nbd);
> -		blk_mq_start_request(req);
>  		return -EINVAL;
>  	}
>  	cmd->status = BLK_STS_OK;
> @@ -967,7 +965,6 @@ static int nbd_handle_cmd(struct nbd_cmd *cmd, int index)
>  			 */
>  			sock_shutdown(nbd);
>  			nbd_config_put(nbd);
> -			blk_mq_start_request(req);
>  			return -EIO;
>  		}

It is basically a partial revert of the following fix, care to add commit log
about why removing these blk_mq_start_request() is safe?

commit 6a468d5990ecd1c2d07dd85f8633bbdd0ba61c40
Author: Josef Bacik <jbacik@...com>
Date:   Mon Nov 6 16:11:58 2017 -0500

    nbd: don't start req until after the dead connection logic



Thanks, 
Ming