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 <[email protected]>
Signed-off-by: Jianchao Wang <[email protected]>
---
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);
--
2.7.4
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 <[email protected]>
> Signed-off-by: Jianchao Wang <[email protected]>
> ---
> 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.
Bart.
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 <[email protected]>
>> Signed-off-by: Jianchao Wang <[email protected]>
>> ---
>> 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.
>
On Tue, 2018-02-27 at 11:28 +0800, jianchao.wang wrote:
> 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.
Hello Jianchao,
For the legacy block layer preparing and unpreparing a request happens from
inside the block layer core. Please have a look at block/blk-core.c and the
code in that file that handles the request flag RQF_DONTPREP.
Thanks,
Bart.
Hi Bart
Thanks for your kindly response.
On 02/27/2018 11:41 AM, Bart Van Assche wrote:
> On Tue, 2018-02-27 at 11:28 +0800, jianchao.wang wrote:
>> 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.
>
> Hello Jianchao,
>
> For the legacy block layer preparing and unpreparing a request happens from
> inside the block layer core. Please have a look at block/blk-core.c and the
> code in that file that handles the request flag RQF_DONTPREP.
Yes, thanks for your directive.
On the other hand, this patch is to align the actions between blk-mq and block legacy code in __scsi_queue_insert.
As we know, __scsi_queue_insert is just to requeue the request back to queue, as the block legacy code segment above:
for block legacy, it just blk_requeue_request for the request and kick the queue run.
However, for the blk-mq, scsi_mq_requeue_cmd will be invoked, it not only requeue the request, but also unprep request.
This is not what __scsi_queue_insert should do, but scsi_io_completion.
When the request is not finished completely, and scsi_io_completion finds it need a ACTION_REPREP, at the moment,
we need requeue and unprep there.
If I missed something, please feel free to point out. :)
Thanks
Jianchao
>
> Thanks,
>
> Bart.
>
>
>
On Tue, 2018-02-27 at 12:00 +0800, jianchao.wang wrote:
> On the other hand, this patch is to align the actions between blk-mq and block
> legacy code in __scsi_queue_insert.
Hello Jianchao,
Since the legacy SCSI core unpreps an reprepares a request when requeuing it I
think your patch does not align the blk-mq and legacy block layer actions but
instead makes the behavior of the two code paths different.
Thanks,
Bart.
Hi Bart
Thanks for your kindly response.
On 02/27/2018 01:12 PM, Bart Van Assche wrote:
> On Tue, 2018-02-27 at 12:00 +0800, jianchao.wang wrote:
>> On the other hand, this patch is to align the actions between blk-mq and block
>> legacy code in __scsi_queue_insert.
>
> Hello Jianchao,
>
> Since the legacy SCSI core unpreps an reprepares a request when requeuing it I
> think your patch does not align the blk-mq and legacy block layer actions but
> instead makes the behavior of the two code paths different.
>
Can you share more details about this ?
Thanks
Jianchao
On Tue, 2018-02-27 at 13:15 +0800, jianchao.wang wrote:
> Can you share more details about this ?
After having had another look, I think your patch is fine. So if you want you
can add:
Reviewed-by: Bart Van Assche <[email protected]>
On Tue, 2018-02-27 at 17:06 +0000, Bart Van Assche wrote:
> On Tue, 2018-02-27 at 13:15 +0800, jianchao.wang wrote:
> > Can you share more details about this ?
>
> After having had another look, I think your patch is fine.
(replying to my own e-mail)
What I think is fine in your patch is that it skips the unprep and reprep
when requeueing. However, there is a put_device(&sdev->sdev_gendev) call
in scsi_mq_requeue_cmd() and your patch causes that put_device() call to
be skipped when requeueing. An explanation is needed in the commit message
why you think that removing that put_device() call is fine.
Bart.
Hi Bart
Thanks for your kindly response and precious time to review this.
On 02/28/2018 01:18 AM, Bart Van Assche wrote:
> On Tue, 2018-02-27 at 17:06 +0000, Bart Van Assche wrote:
>> On Tue, 2018-02-27 at 13:15 +0800, jianchao.wang wrote:
>>> Can you share more details about this ?
>>
>> After having had another look, I think your patch is fine.
>
> (replying to my own e-mail)
>
> What I think is fine in your patch is that it skips the unprep and reprep
> when requeueing. However, there is a put_device(&sdev->sdev_gendev) call
> in scsi_mq_requeue_cmd() and your patch causes that put_device() call to
> be skipped when requeueing. An explanation is needed in the commit message
> why you think that removing that put_device() call is fine.
Your concern is right.
For the block legacy path in scsi core, the get_device(&sdev->sdev_gendev) is in prep.
So when it requeue the request w/ RQF_DONTPREP, the reference will not be got again.
However, for blk-mq patch in scsi core, the get_device(&sdev->sdev_gendev) in .get_budget,
so put_device is still needed here.
Thanks for your directive.
Jianchao