linux-ext4 - Re: 2.6.35-r5 ext3 corruptions

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Message-ID: <20100721063222.GW32635@dastard>
Date:	Wed, 21 Jul 2010 16:32:22 +1000
From:	Dave Chinner <david@...morbit.com>
To:	linux-ext4@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org
Subject: Re: 2.6.35-r5 ext3 corruptions

On Tue, Jul 20, 2010 at 08:45:12AM +1000, Dave Chinner wrote:
> On Thu, Jul 15, 2010 at 08:57:45PM +1000, Dave Chinner wrote:
> > Upgrading my test vms from 2.6.35-rc3 to 2.6.35-rc5 is resulting in
> > repeated errors on the root drive of a test VM:
> > 
> > { 1532.368808] EXT3-fs error (device sda1): ext3_lookup: deleted inode referenced: 211043
> > [ 1532.370859] Aborting journal on device sda1.
> > [ 1532.376957] EXT3-fs (sda1): 
> > [ 1532.376976] EXT3-fs (sda1): error: ext3_journal_start_sb: Detected aborted journal
> > [ 1532.376980] EXT3-fs (sda1): error: remounting filesystem read-only
> > [ 1532.420361] error: remounting filesystem read-only
> > [ 1532.621209] EXT3-fs error (device sda1): ext3_lookup: deleted inode referenced: 211043
> > 
> > The filesysetm is a mess when checked on reboot - lots of illegal
> > references to blocks, multiply linked blocks, etc, but repairs.
> > Files are lots, truncated, etc, so there is visible filesystem
> > damage.
> > 
> > I did lots of testing on 2.6.35-rc3 and came across no problems;
> > problems only seemed to start with 2.6.35-rc5, and I've reproduced
> > the problem on a vanilla 2.6.35-rc4.
> > 
> > The problem seems to occur randomly - sometimes during boot or when
> > idle after boot, sometimes a while after boot. I haven't done any
> > digging at all for the cause - all I've done so far is confirm that
> > it is reproducable and it's not my code causing the problem.
> 
> Looks like this problem was isolated to a single VM and root
> filesystem. I could not reproduce it on anything other than the
> one filesystem that was failing.

Ok, so now I know *why* that one filesystem got busted - I built a
kernel without CONFIG_EXT3_DEFAULTS_TO_ORDERED set and it got a
forced reboot (echo b > proc/sysrq-trigger). That'll teach me for
trying to reproduce bugs Andrew is tripping over with his config
files.

Quite frankly, data=writeback mode for ext3 is a dangerous,
dangerous configuration to run by default. IMO, it shouldn't be the
default. Patch below.

Cheers,

Dave.

-- 
Dave Chinner
david@...morbit.com

ext3: default to ordered mode

From: Dave Chinner <dchinner@...hat.com>

data=writeback mode is dangerous and is leads to filesystem
corruption, data loss and stale data exposure when systems crash. It
should not be the default, especially when all major distros ensure
their ext3 filesystems default to ordered mode. Change the default
mode to the safer data=ordered mode, because we should be caring
far more about avoiding corruption than performance.

Signed-off-by: Dave Chinner <dchinner@...hat.com>
---
 fs/ext3/Kconfig |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/fs/ext3/Kconfig b/fs/ext3/Kconfig
index 522b154..e8c6ba0 100644
--- a/fs/ext3/Kconfig
+++ b/fs/ext3/Kconfig
@@ -31,6 +31,7 @@ config EXT3_FS
 config EXT3_DEFAULTS_TO_ORDERED
 	bool "Default to 'data=ordered' in ext3"
 	depends on EXT3_FS
+	default y
 	help
 	  The journal mode options for ext3 have different tradeoffs
 	  between when data is guaranteed to be on disk and
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