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Message-ID: <20140711001334.GF10417@birch.djwong.org> Date: Thu, 10 Jul 2014 17:13:34 -0700 From: "Darrick J. Wong" <darrick.wong@...cle.com> To: "Theodore Ts'o" <tytso@....edu> Cc: Matteo Croce <technoboy85@...il.com>, Eric Whitney <enwlinux@...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 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! --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 > > >> -- > > >> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > > >> the body of a message to majordomo@...r.kernel.org > > >> More majordomo info at http://vger.kernel.org/majordomo-info.html > > > > > > > > -- > > Matteo Croce > > OpenWrt Developer > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > > the body of a message to majordomo@...r.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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