mp_lock related panic (it seems)

[Rumko <rumcic@xxxxxxxxx>]

http://www.rumko.net/dragonfly/DSC00129.JPG

because after a reboot savecore says there were no core dumps, I can only
provide this picture for now.

It does not occur on every reboot (after the panic, the next time it booted -
and after fsck-ing all partitions -, the machine booted up properly).

How should I start debugging this?
-- 
Regards,
Rumko