Re: [PATCH V3] scsi: core: use blk_mq_requeue_request in __scsi_queue_insert

[jianchao.wang]

Hi Bart

Thanks for your kindly response and directive.

On 03/03/2018 12:31 AM, Bart Van Assche wrote:
> On Fri, 2018-03-02 at 11:31 +0800, Jianchao Wang wrote:
>> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
>> index a86df9c..d2f1838 100644
>> --- a/drivers/scsi/scsi_lib.c
>> +++ b/drivers/scsi/scsi_lib.c
>> @@ -191,7 +191,13 @@ 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);
>> +/*
>> + * scsi_device.sdev_gendev will be get every time in 
>> .get_budget and
>> + * be put in scsi_end_request. Hence we need to put the 
>> reference
>> + * here when we decide to requeue request.
>> + */
>> +blk_mq_requeue_request(cmd->request, true);
>> +put_device(&device->sdev_gendev);
>>  return;
>>  }
>>  spin_lock_irqsave(q->queue_lock, flags);
> 
> Please consider to change the new comment into something like the following:
> "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."

Yes, your comment is more detailed and clearly.

Sincerely
Jianchao

Re: [PATCH V3] scsi: core: use blk_mq_requeue_request in __scsi_queue_insert

[Bart Van Assche]

On Fri, 2018-03-02 at 11:31 +0800, Jianchao Wang wrote:
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index a86df9c..d2f1838 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -191,7 +191,13 @@ 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);
> + /*
> +  * scsi_device.sdev_gendev will be get every time in 
> .get_budget and
> +  * be put in scsi_end_request. Hence we need to put the 
> reference
> +  * here when we decide to requeue request.
> +  */
> + blk_mq_requeue_request(cmd->request, true);
> + put_device(&device->sdev_gendev);
>   return;
>   }
>   spin_lock_irqsave(q->queue_lock, flags);

Please consider to change the new comment into something like the following:
"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."

Thanks,

Bart.