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[bisected] xfs panics when attempting to mount btrfs

To: Dave Chinner <dchinner@xxxxxxxxxx>, Phil White <pwhite@xxxxxxx>, Ben Myers <bpm@xxxxxxx>
Subject: [bisected] xfs panics when attempting to mount btrfs
From: Sergei Trofimovich <slyfox@xxxxxxxxxx>
Date: Sat, 29 Dec 2012 13:52:29 +0300
Cc: xfs@xxxxxxxxxxx, Alex Elder <elder@xxxxxxxxxx>
Organization: VBA Ltd.
Sorry for not providing exact logs,
I have got a problem at boot.

The problem is the following:

I have a / as btrfs filesystem and have quite a few
filesystems built-in to kernel [1]

Thus when root is mounted each filesystem is probed.
After 3.8-rc1 my box stopped booting showing kernel panic.
Panic said there is no valid filesystem on my devices

Panic showed all my drives and partitions which means
they were detected correctly.

Bisection shown the following commit 98021821a502db347bd9c7671beeee6e8ce07ea6 

> xfs: verify superblocks as they are read from disk

which looks very likely to cause troubles.

I think it's easy to reproduce problems
by trying to mount something non-xfs as xfs
(didn't try but will do if you like).

    mount -t xfs -oloop /some/btrfs.image


$ cat /proc/filesystems  | grep -v nodev


98021821a502db347bd9c7671beeee6e8ce07ea6 is the first bad commit
commit 98021821a502db347bd9c7671beeee6e8ce07ea6
Author: Dave Chinner <dchinner@xxxxxxxxxx>
Date:   Mon Nov 12 22:54:03 2012 +1100

    xfs: verify superblocks as they are read from disk
    Add a superblock verify callback function and pass it into the
    buffer read functions. Remove the now redundant verification code
    that is currently in use.
    Adding verification shows that secondary superblocks never have
    their "sb_inprogress" flag cleared by mkfs.xfs, so when validating
    the secondary superblocks during a grow operation we have to avoid
    checking this field. Even if we fix mkfs, we will still have to
    ignore this field for verification purposes unless a version of mkfs
    that does not have this bug was used.
    Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
    Reviewed-by: Phil White <pwhite@xxxxxxx>
    Signed-off-by: Ben Myers <bpm@xxxxxxx>

:040000 040000 56723c8ba61cafeaf85782b3f378b3248afab7e1
cfba7b784fa9016de85017952fd1c5960e4655ce M      fs



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