XFS Freezing occasionally hangs

[Ryan Campbell]

We use XFS on EC2 EBS running on Arch Linux (kernel 3.6.7-1-ARCH). Before
we take an EC2 snapshot, we call xfs_freeze on the mount so that we can
have a consistent snapshot.

On instances running for around 30 days, we see the XFS freeze hang,
resulting in a skyrocketing load (but not CPU). We can't kill the
xfs_freeze process. The only route available is usually to force a reboot
of the server without cleaning unmounting.

There are backtraces in dmesg complaining both of hung xfs processes, and
hung java processes. https://gist.github.com/3d46830eac52df44d30f

Is this a known issue? We call xfs_freeze quite often on thousands of XFS
volumes, so I wouldn't be surprised if we have encountered an edge case
considering how often we do this.

Any help appreciated. I'm recampbell on #xfs/freenode.

Thanks,
Ryan
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