Deterministic unionfs panic triggered by kern_renameat() on 8.2-STABLE

[Lawrence Stewart]

Hi all,

I'm playing around with the changes to the ISO building infrastructure
which Nathan Whitehorn has most recently been tweaking. I've built an
ISO which runs as its first rc.d script the set of commands to create a
unionfs over the top of the read only /etc. This is obviously desirable
as it allows anything which attempts to write to /etc (e.g. hostid,
sshd, dhclinet) to work transparently.

Everything works great - system rc.d startup works, I can create files
in /etc, edit existing files using ee, run dhclient without any command
line switches etc.

However, when I use vim to edit a file, it obviously uses a different
syscall (kern_renameat) to any of the other programs I've tested, which
triggers a deterministic panic. A screenshot of the panic from
virtualbox and a basic reproduction recipe are available at [1].

Any thoughts on how to fix the locking?

Cheers,
Lawrence

[1] http://people.freebsd.org/~lstewart/misc/unionfs_debug/