Panic - ffs_valloc: dup alloc

[Chris Torek]

For what (little :-) ) it's worth, I got bit by this too.  Ultimately it
boils down to the problem that once the on-disk file system is sufficiently
broken, the journal doesn't have enough information for fsck to even detect
the problem, much less fix it.

(In my case the problem most likely was created by a bad bit in RAM.  That
particular hardware has no ECC.)

It seems to me that certain UFS panics (including "dup alloc", which was
the one getting me too if I remember right) should poison the journal to
force a full fsck.  This won't necessarily solve everything, but it would
at least carry the problem detection forward from the kernel into fsck...

Chris