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

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Date:   Tue, 27 Feb 2018 11:28:46 +0800
From:   "jianchao.wang" <jianchao.w.wang@...cle.com>
To:     Bart Van Assche <Bart.VanAssche@....com>,
        "jejb@...ux.vnet.ibm.com" <jejb@...ux.vnet.ibm.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>
Cc:     "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "hch@....de" <hch@....de>
Subject: Re: [PATCH] scsi: core: use blk_mq_requeue_request in
 __scsi_queue_insert

Hi Bart

Thanks for your kindly response.

On 02/27/2018 11:08 AM, Bart Van Assche wrote:
> On Mon, 2018-02-26 at 15:58 +0800, 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,
>> just use blk_mq_requeue_request with kick_requeue_list == true.
>>
>> Cc: Christoph Hellwig <hch@....de>
>> Signed-off-by: Jianchao Wang <jianchao.w.wang@...cle.com>
>> ---
>>  drivers/scsi/scsi_lib.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
>> index a86df9c..06d8110 100644
>> --- a/drivers/scsi/scsi_lib.c
>> +++ b/drivers/scsi/scsi_lib.c
>> @@ -191,7 +191,7 @@ 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);
>> +		blk_mq_requeue_request(cmd->request, true);
>>  		return;
>>  	}
>>  	spin_lock_irqsave(q->queue_lock, flags);
> 
> I think this patch will break the code in the aacraid driver that iterates
> over sdev->cmd_list because commands are added to and removed from that
> list in the prep / unprep code.

If that is true, what if aacraid driver uses block legacy instead of blk-mq ?
w/ blk-mq disabled, __scsi_queue_insert just requeue the request with blk_requeue_request.

__scsi_queue_insert
...
	if (q->mq_ops) {
		scsi_mq_requeue_cmd(cmd);
		return;
	}
	spin_lock_irqsave(q->queue_lock, flags);
	blk_requeue_request(q, cmd->request);
	kblockd_schedule_work(&device->requeue_work);
	spin_unlock_irqrestore(q->queue_lock, flags);
...

no prep/unprep code there for block legacy code.

Thanks
Jianchao

> 
> Bart.
>