linux-kernel - Re: [PATCH V4] scsi: core: use blk_mq_requeue_request in __scsi_queue

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Date:   Tue, 6 Mar 2018 22:39:38 +0800
From:   "jianchao.wang" <jianchao.w.wang@...cle.com>
To:     jejb@...ux.vnet.ibm.com, martin.petersen@...cle.com
Cc:     Bart.VanAssche@....com, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org, Christoph Hellwig <hch@....de>
Subject: Re: [PATCH V4] scsi: core: use blk_mq_requeue_request in
 __scsi_queue_insert

Hi Martin

Can you take your precious time to review this ?

Thanks in advice.
Jianchao

On 03/03/2018 09:54 AM, Jianchao Wang wrote:
> In scsi core, __scsi_queue_insert should just put request back on
> the queue and retry using the same command as before. However, for
> blk-mq, scsi_mq_requeue_cmd is employed here which will unprepare
> the request. To align with the semantics of __scsi_queue_insert,
> use blk_mq_requeue_request with kick_requeue_list == true and put
> the reference of scsi_device.
> 
> Cc: Christoph Hellwig <hch@....de>
> Signed-off-by: Jianchao Wang <jianchao.w.wang@...cle.com>
> Reviewed-by: Bart Van Assche <bart.vanassche@....com>
> ---
> Changelog:
> V3 -> V4:
>  - modify the comment and make it more clearly
> 
> V2 -> V3:
>  - add comment to explain why we need a put_device in
>    __scsi_queue_insert
>  - add reviewed-by
> 
> V1 -> V2:
>  - add put_device on scsi_device->sdev_gendev
>  drivers/scsi/scsi_lib.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index a86df9c..6ce33f6 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -191,7 +191,19 @@ static void __scsi_queue_insert(struct scsi_cmnd *cmd, int reason, bool unbusy)
>  	 */
>  	cmd->result = 0;
>  	if (q->mq_ops) {
> -		scsi_mq_requeue_cmd(cmd);
> +		/*
> +		 * Before a SCSI command is dispatched,
> +		 * get_device(&sdev->sdev_gendev) is called and the host,
> +		 * target and device busy counters are increased. Since
> +		 * requeuing a request causes these actions to be repeated and
> +		 * since scsi_device_unbusy() has already been called,
> +		 * put_device(&device->sdev_gendev) must still be called. Call
> +		 * put_device() after blk_mq_requeue_request() to avoid that
> +		 * removal of the SCSI device can start before requeueing has
> +		 * happened.
> +		 */
> +		blk_mq_requeue_request(cmd->request, true);
> +		put_device(&device->sdev_gendev);
>  		return;
>  	}
>  	spin_lock_irqsave(q->queue_lock, flags);
>