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

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Date:	Tue, 8 Mar 2016 14:20:34 +0100
From:	Hannes Reinecke <hare@...e.de>
To:	Yaniv Gardi <ygardi@...eaurora.org>,
	James.Bottomley@...senPartnership.com
Cc:	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 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 however its tag is no longer valid.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...

Cheers,

Hannes-
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@...e.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
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