linux-ext4 - Kernel panic from corrupt journal

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Date:	Thu, 30 Aug 2012 10:22:12 +0100
From:	Brian Candler <B.Candler@...ox.com>
To:	linux-ext4@...r.kernel.org
Subject: Kernel panic from corrupt journal

I have a system where just replaying the journal causes a kernel panic. If I
boot into recovery mode and then type

    # fsck -y /dev/sda8

it says it's recovering the journal, then a second or two later I get a
panic traceback.  Unfortunately there are only 24 lines displayed on the
screen; my scribbled notes give the top and bottom ones as

    req_bios_endio.isra.45+0xa3/0xe0
    ...
    start_secondary+0xd8/0xdb

I can get a screenshot of this if it's useful to anyone.

With "debugfs /dev/sda8", then:

    logdump /tmp/sda8.dmp      -> this works OK, writes out a list of blocks
    logdump -ac /tmp/sda8.dmp  -> this also causes a kernel panic!

So:

(1) the fact that I can cause a kernel panic is a bug, and if I can help fix
it I will; however I'm not sure how I can pass on any useful information
given that even dumping the journal causes a kernel panic.  Can I get the
journal by dd'ing at a specific offset?

(2) I'd also like to be able to recover this filesystem, e.g. by clearing
the journal, but I haven't been able to find out how to do this.

The best I can find by googling is to try mounting with ro,noload. I'll give
this a go to see if I can backup the filesystem, but otherwise it looks like
I may have to reformat the partition and restore.

Background info: this system is a Dell Zino HD running Ubuntu 12.04 (fully
patched as of 29 Aug 2012, standard 3.2.0-xx kernel).  My wife accidentally
chose "suspend" rather than "shutdown" to turn it off yesterday, and it
failed to boot this morning.

Regards,

Brian.
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