linux-kernel - Re: [v3.7 Regression] [SCSI] sd: Implement support for WRITE SAME

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Date:	Fri, 14 Dec 2012 21:38:14 -0500
From:	Joseph Salisbury <joseph.salisbury@...onical.com>
To:	Mike Snitzer <snitzer@...hat.com>
CC:	martin.petersen@...cle.com,
	Kernel Team <kernel-team@...ts.ubuntu.com>,
	linux-kernel@...r.kernel.org, jgarzik@...hat.com,
	JBottomley@...allels.com, Milan Broz <mbroz@...hat.com>
Subject: Re: [v3.7 Regression]  [SCSI] sd: Implement support for WRITE SAME

On 12/14/2012 04:11 PM, Mike Snitzer wrote:
> On Fri, Dec 14 2012 at  3:30pm -0500,
> Joseph Salisbury <joseph.salisbury@...onical.com> wrote:
>
>> Hi Martin,
>>
>> A bug was opened against the Ubuntu kernel[0].  After a kernel
>> bisect, it was found that reverting the following commit resolved
>> this bug:
>>
>> commit 5db44863b6ebbb400c5e61d56ebe8f21ef48b1bd
>> Author: Martin K. Petersen <martin.petersen@...cle.com>
>> Date:   Tue Sep 18 12:19:32 2012 -0400
>> [SCSI] sd: Implement support for WRITE SAME
>>
>> The regression was introduced as of v3.7-rc7.
>>
>> The bug can be reproduced with the following commands, which will
>> operate on a virtual scsi_debug device, so they won't change any
>> data on the test system. However, this will completely crash the
>> system:
>>
>> sudo modprobe scsi_debug
>> sudo luksformat -t ext4 /dev/sdb <- Or whatever device gets assigned
>> after inserting scsi_debug.
>> sudo cryptsetup luksOpen /dev/sdb treasure
>>
>> Everything works fine up to here, but the following will cause the crash:
>>
>> sudo mount /dev/mapper/treasure /mnt
>>
>> The bug can be reproduced on bare metal, in a VM and on i386 or amd64.
>>
>> I see that you are the author of this patch, so I wanted to run this
>> by you.  I was thinking of requesting a revert for v3.7, but I
>> wanted to get your feedback first.
>>
>>
>> Thanks,
>>
>> Joe
>>
>>
>> [0] https://bugs.launchpad.net/bugs/1089818
> The WRITE SAME change was introduced long before v3.7-rc7.  I think your
> bisect is somehow wrong.
 From Linus' tree:
git describe --contains 5db4486
v3.7-rc7~19^2

Reverting commit 5db4486 solves the bug previously mentioned.

>
> Milan Broz recently pointed out issues he found with luks when using a
> late 3.7-rc (rc7 afaik).  Linus fixed that issue with this commit (which
> landed in the final v3.7):
> http://git.kernel.org/linus/684c9aaebbb0ea3a9954
>
> That may not be _the_ problem though.  But have you tried the final
> v3.7?

Yes, v3.7 without reverting 5db4486 exhibits the bug.

>
> Mike
I'll research further and provide additional data.
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