linux-kernel - Re: [PATCH v7 03/17] scsi: ufs: implement scsi host timeout handler

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Message-ID: <56DFC661.1020706@suse.de>
Date:	Wed, 9 Mar 2016 07:44:49 +0100
From:	Hannes Reinecke <hare@...e.de>
To:	ygardi@...eaurora.org
Cc:	james.bottomley@...senpartnership.com,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, santoshsy@...il.com,
	linux-scsi-owner@...r.kernel.org,
	Gilad Broner <gbroner@...eaurora.org>,
	Vinayak Holikatti <vinholikatti@...il.com>,
	"James E.J. Bottomley" <jbottomley@...n.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>
Subject: Re: [PATCH v7 03/17] scsi: ufs: implement scsi host timeout handler

On 03/08/2016 08:58 PM, ygardi@...eaurora.org wrote:
>> On 03/08/2016 02:01 PM, Hannes Reinecke wrote:
>>> On 03/08/2016 01:35 PM, Yaniv Gardi wrote:
>>>> A race condition exists between request requeueing and scsi layer
>>>> error handling:
>>>> When UFS driver queuecommand returns a busy status for a request,
>>>> it will be requeued and its tag will be freed and set to -1.
>>>> At the same time it is possible that the request will timeout and
>>>> scsi layer will start error handling for it. The scsi layer reuses
>>>> the request and its tag to send error related commands to the device,
>>>> however its tag is no longer valid.
>>>> As this request was never really sent to the device, there is no
>>>> point to start error handling with the device.
>>>> Implement the scsi error handling timeout callback and bypass SCSI
>>>> error handling for request that were not actually sent to the device.
>>>> For such requests simply reset the block layer timer. Otherwise, let
>>>> SCSI layer perform the usual error handling.
>>>>
>>>> Reviewed-by: Dolev Raviv <draviv@...eaurora.org>
>>>> Signed-off-by: Gilad Broner <gbroner@...eaurora.org>
>>>> Signed-off-by: Yaniv Gardi <ygardi@...eaurora.org>
>>>>
>>>> ---
>>>>  drivers/scsi/ufs/ufshcd.c | 36 ++++++++++++++++++++++++++++++++++++
>>>>  1 file changed, 36 insertions(+)
>>>>
>>> Having a timeout handler is always a good idea, even though this
>>> doesn't do anything here.
>>> Are we sure that the requests will return eventually?
>>> Does the UFS spec provide for a command abort?
>>>
>> In fact, looking at the UFS spec there _is_ a command abort.
>> I would recommend implementing a task management request UPIO with
>> type 'ABORT TASK' here for any task found to be pending.
>> In the end, you might run into a _valid_ timeout, at which point you
>> really want to abort the command...
>>
> 
> but this is not what we'd like to achieve.
> we don't want to abort a task that was not even dispatched to the UFS driver.
> in those cases we need to re-queue the request and reset the timer.
> 
Fully understood.

> Hannes, i appreciate your time, but I really don't understand why you
> insist on coming up with suggestions, when we already implemented one that
> is working. more over, your solution doesn't fix the race condition which is the
> reason for this patch.
> as i don't have HW to test anything at the moment, I think it's better to
> stick with this solution that also fix the BUG and also was verified and
> tested.
> 
Ah. Didn't know that. I was under the impression that you _had_ the
hardware available. If not then of course it's not easy to verify
anything.

So, all things considered:

Reviewed-by: Hannes Reinecke <hare@...e.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@...e.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
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