linux-ext4 - Re: Add ext4__allow_read-only_mounts_with_corrupted_block_group

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Date:	Wed, 16 Jul 2008 03:29:14 -0600
From:	Andreas Dilger <adilger@....com>
To:	Gary Hawco <ghawco@....net>
Cc:	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	Theodore Tso <tytso@....edu>
Subject: Re: Add
	ext4__allow_read-only_mounts_with_corrupted_block_group_checksums	patch

On Jul 15, 2008  19:31 +0000, Gary Hawco wrote:
> Just recompiled 2.6.26 with the newest snapshot (15-July 2008/2310GMT).
> uninit_bg had been enabled.
> 
> To test kernel I did: tune2fs -O ^uninit_bg /dev/sda6 to remove uninit_bg
> feature.
> Was prompted to run e2fsck on system.
> 
> Rebooted and e2fsck saw errors and did a forced fsck without having to
> reboot. All is well thus far.

You shouldn't really have rebooted at that point, just run e2fsck on
the filesystem to clear the checksums.

> Then I did the reverse: tune2fs -O uninit_bg /dev/sda6 to renable uninit_bg
> feature.  Again, I was prompted to run e2fsck on system.

Again, you should have just run e2fsck on the filesystem without rebooting,
in order to update the checksums.

> Rebooted. This time I got a kernel panic that started with:
> EXT4-fs: ext4_check_descriptors: Checksum for group 2 failed (10368!=32990)
> EXT4-fs: group descriptors corrupted!

The kernel thinks the filesystem is corrupted, so a full e2fsck needs to
be run.  However, e2fsck is probably sitting on that unmountable filesystem.

> I was under the impression that the newest patch would handle this or am I
> mistaken?

We probably need to allow the kernel to mount the filesystem read-only in
this case in order to run e2fsck.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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