Date:	Fri, 11 Jul 2014 17:50:34 +0900
From:	Jaehoon Chung <jh80.chung@...sung.com>
To:	Eric Whitney <enwlinux@...il.com>,
	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	Theodore Ts'o <tytso@....edu>,
	Matteo Croce <technoboy85@...il.com>,
	David Jander <david@...tonic.nl>,
	Dmitry Monakhov <dmonakhov@...nvz.org>,
	linux-ext4@...r.kernel.org, Azat Khuzhin <a3at.mail@...il.com>
Subject: Re: ext4: journal has aborted

On 07/11/2014 09:45 AM, Eric Whitney wrote:
> * Darrick J. Wong <darrick.wong@...cle.com>:
>> On Thu, Jul 10, 2014 at 06:32:45PM -0400, Theodore Ts'o wrote:
>>> To be clear, what you would need to do is to revert commit
>>> 007649375f6af242d5b1df2c15996949714303ba to prevent the fs corruption.
>>> Darrick's patch is one that tries to fix the problem addressed by that
>>> commit in a different fashion.
>>>
>>> Quite frankly, reverting the commit, which is causing real damage, is
>>> far more impotrant to me right now than what to do in order allow
>>> CONFIG_EXT4FS_DEBUG to work (which is nice, but it's only something
>>> that file system developers need, and to be honest I can't remember
>>> the last time I've used said config option).  But if we know that
>>> Darrick's fix works, I'm willing to push that to Linus at the same
>>> time that I push a revert of 007649375f6af242d5b1df2c15996949714303ba
>>
>> Reverting the 007649375... patch doesn't seem to create any obvious regressions
>> on my test box (though again, I was never able to reproduce it as consistently
>> as Eric W.).
>>
>> Tossing in the [1] patch also fixes the crash when CONFIG_EXT4_DEBUG=y on
>> 3.16-rc4.  I'd say it's safe to send both to Linus and stable.
>>
>> If anyone experiences problems that I'm not seeing, please yell loudly and
>> soon!
>>
> 
> Reverting the suspect patch - 007649375f - on 3.16-rc3 and running on the
> Panda yielded 10 successive "successful" generic/068 failures (no block
> bitmap trouble on reboot).  So, it looks like that patch is all of it.
In my case, after reverting it, i didn't find the bitmap corrupt problem at exynos board.
Before reverting it, when i try to reboot, it occurred the problem at almost every time.
(Kernel version is 3.16-rv4, eMMC5.0 card is used.)

Best Regards,
Jaehoon Chung
> 
> Running the same test scenario on Darrick's patch (CONFIG_EXT4FS_DEBUG =>
> CONFIG_EXT4_DEBUG) applied to 3.16-rc3 lead to exactly the same result.
> No panics, BUGS, or other misbehavior whether generic/068 completed 
> successfully or failed (and that test used here simply because it was
> convenient) and no trouble on boot, etc.
> 
> Let me know if anything else is needed.
> 
> Eric
> 
>> --D
>>
>> [1] http://www.spinics.net/lists/linux-ext4/msg43287.html
>>>
>>> Cheers,
>>>
>>> 						- Ted
>>>
>>> On Thu, Jul 10, 2014 at 11:31:14PM +0200, Matteo Croce wrote:
>>>> Will do, thanks!
>>>>
>>>> 2014-07-10 22:01 GMT+02:00 Darrick J. Wong <darrick.wong@...cle.com>:
>>>>> On Thu, Jul 10, 2014 at 02:57:48PM -0400, Eric Whitney wrote:
>>>>>> * Theodore Ts'o <tytso@....edu>:
>>>>>>> On Mon, Jul 07, 2014 at 11:53:10AM -0400, Theodore Ts'o wrote:
>>>>>>>> An update from today's ext4 concall.  Eric Whitney can fairly reliably
>>>>>>>> reproduce this on his Panda board with 3.15, and definitely not on
>>>>>>>> 3.14.  So at this point there seems to be at least some kind of 3.15
>>>>>>>> regression going on here, regardless of whether it's in the eMMC
>>>>>>>> driver or the ext4 code.  (It also means that the bug fix I found is
>>>>>>>> irrelevant for the purposes of working this issue, since that's a much
>>>>>>>> harder to hit, and that bug has been around long before 3.14.)
>>>>>>>>
>>>>>>>> The problem in terms of narrowing it down any further is that the
>>>>>>>> Pandaboard is running into RCU bugs which makes it hard to test the
>>>>>>>> early 3.15-rcX kernels.....
>>>>>>>
>>>>>>> In the hopes of making it easy to bisect, I've created a kernel branch
>>>>>>> which starts with 3.14, and then adds on all of the ext4-related
>>>>>>> commits since then.   You can find it at:
>>>>>>>
>>>>>>> git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git test-mb_generate_buddy-failure
>>>>>>>
>>>>>>> https://git.kernel.org/cgit/linux/kernel/git/tytso/ext4.git/log/?h=test-mb_generate_buddy-failure
>>>>>>>
>>>>>>> Eric, can you see if you can repro the failure on your Panda Board?
>>>>>>> If you can, try doing a bisection search on these series:
>>>>>>>
>>>>>>> git bisect start
>>>>>>> git bisect good v3.14
>>>>>>> git bisect bad test-mb_generate_buddy-failure
>>>>>>>
>>>>>>> Hopefully if it is caused by one of the commits in this series, we'll
>>>>>>> be able to pin point it this way.
>>>>>>
>>>>>> First, the good news (with luck):
>>>>>>
>>>>>> My testing currently suggests that the patch causing this regression was
>>>>>> pulled into 3.15-rc3 -
>>>>>>
>>>>>> 007649375f6af242d5b1df2c15996949714303ba
>>>>>> ext4: initialize multi-block allocator before checking block descriptors
>>>>>>
>>>>>> Bisection by selectively reverting ext4 commits in -rc3 identified this patch
>>>>>> while running on the Pandaboard.  I'm still using generic/068 as my reproducer.
>>>>>> It occasionally yields a false negative, but it has passed 10 consecutive
>>>>>> trials on my revert/bisect kernel derived from 3.15-rc3.  Given the frequency
>>>>>> of false negatives I've seen, I'm reasonably confident in that result.  I'm
>>>>>> going to run another series with just that patch reverted on 3.16-rc3.
>>>>>>
>>>>>> Looking at the patch, the call to ext4_mb_init() was hoisted above the code
>>>>>> performing journal recovery in ext4_fill_super().  The regression occurs only
>>>>>> after journal recovery on the root filesystem.
>>>>>
>>>>> Thanks for finding the culprit! :)
>>>>>
>>>>> Can you apply this patch, build with CONFIG_EXT4FS_DEBUG=y, and see if an
>>>>> FS will mount without crashing?  This was the cruddy patch I sent in (and later
>>>>> killed) that fixed the crash on mount with EXT4FS_DEBUG in a somewhat silly
>>>>> way.  Maybe it's appropriate now.
>>>>> http://www.spinics.net/lists/linux-ext4/msg43287.html
>>>>>
>>>>> --D
>>>>>
>>>>>>
>>>>>> Secondly:
>>>>>>
>>>>>> Thanks for that git tree!  However, I discovered that the same "RCU bug" I
>>>>>> thought I was seeing on the Panda was also visible on the x86_64 KVM, and
>>>>>> it was actually just RCU noticing stalls.  These also occurred when using
>>>>>> your git tree as well as on mainline 3.15-rc1 and 3.15-rc2 and during
>>>>>> bisection attempts on 3.15-rc3 within the ext4 patches, and had the effect of
>>>>>> masking the regression on the root filesystem.  The test system would lock up
>>>>>> completely - no console response - and made it impossible to force the reboot
>>>>>> which was required to set up the failure.  Hence the reversion approach, since
>>>>>> RCU does not report stalls in 3.15-rc3 (final).
>>>>>>
>>>>>> Eric
>>>>>>
>>>>>>
>>>>>>
>>>>>>>
>>>>>>> Thanks!!
>>>>>>>
>>>>>>>                                             - Ted
>>>>>> --
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>>>>
>>>>
>>>>
>>>> -- 
>>>> Matteo Croce
>>>> OpenWrt Developer
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