Re: [PATCH] scsi: core: use blk_mq_requeue_request in __scsi_queue_insert

[jianchao.wang]

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 <h...@lst.de>
>> Signed-off-by: Jianchao Wang <jianchao.w.w...@oracle.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.
>