Date:	Wed, 2 Jul 2014 12:17:52 +0200
From:	David Jander <david@...tonic.nl>
To:	Eric Whitney <enwlinux@...il.com>
Cc:	"Theodore Ts'o" <tytso@....edu>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	"Darrick J. Wong" <darrick.wong@...cle.com>,
	Matteo Croce <technoboy85@...il.com>,
	linux-ext4@...r.kernel.org
Subject: Re: ext4: journal has aborted


Hi Eric,

On Tue, 1 Jul 2014 12:36:46 -0400
Eric Whitney <enwlinux@...il.com> wrote:

> * Theodore Ts'o <tytso@....edu>:
> > On Tue, Jul 01, 2014 at 09:07:27PM +0900, Jaehoon Chung wrote:
> > > Hi,
> > > 
> > > i have interesting for this problem..Because i also found the same problem..
> > > Is it Journal problem?
> > > 
> > > I used the Linux version 3.16.0-rc3.
> > > 
> > > [    3.866449] EXT4-fs error (device mmcblk0p13): ext4_mb_generate_buddy:756: group 0, 20490 clusters in bitmap, 20488 in gd; block bitmap corrupt.
> > > [    3.877937] Aborting journal on device mmcblk0p13-8.
> > > [    3.885025] Kernel panic - not syncing: EXT4-fs (device mmcblk0p13): panic forced after error
> > 
> > This message means that the file system has detected an inconsistency
> > --- specifically, that the number of blocks marked as in use in the
> > allocation bbitmap is different from what is in the block group
> > descriptors.
> > 
> > The file system has been marked to force a panic after an error, at
> > which point e2fsck will be able to repair the inconsistency.
> > 
> > What's not clear is *how* the why this happened.  It can happen simply
> > because of a hardware problem.  (In particular, not all mmc flash
> > devices handle power failures gracefully.)  Or it could be a cosmic,
> > ray, or it might be a kernel bug.
> > 
> > Normally I would chalk this up to a hardware bug, bug it's possible
> > that it is a kernel bug.  If people can reliably reproduce the problem
> > where no power failures or other unclean shutdowns were involved
> > (since the last time file system has been checked using e2fsck) then
> > that would be realy interesting.
> 
> Hi Ted:
> 
> I saw a similar failure during 3.16-rc3 (plus ext4 stable fixes plus msync
> patch) regression on the Pandaboard this morning.  A generic/068 hang
> on data_journal required a reboot for recovery (old bug, though rarer lately).
> On reboot, the root filesystem - default 4K, and on an SD card - went ro
> after the same sort of bad block bitmap / journal abort sequence.  Rebooting
> forced a fsck that cleared up the problem.  The target test filesystem was on
> a USB-attached disk, and it did not exhibit the same problems on recovery.

Please be careful about conclusions from regular SD cards and USB sticks for
mass-storage. Unlike hardened eMMC (4.41+), these COTS mass-storage devices
are not meant for intensive use and can perfectly easily corrupt data out of
themselves. I've seen it happening many times already.

> So, it looks like there might be more than just hardware involved here, 
> although eMMC/flash might be a common denominator.  I'll see if I can come up
> with a reliable reproducer once the regression pass is finished if someone
> doesn't beat me to it.

I agree that there is a strong correlation towards flash-based storage, but I
cannot explain why this factor would make a difference. How are flash-based
block-devices different to ext4 than spinning-disk media (besides trim
support)?

Best regards,

-- 
David Jander
Protonic Holland.
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