FreeBSD 10.0 adaptive mutex with strange mtx_lock value = panic

[Darren Reed]

In debugging a kernel panic running inside a VM, I found the following:

(kgdb) p *$15
$16 = {lock_object = {lo_name = 0xffffffff81a8a224 "filter rule lock",
    lo_flags = 16908288, lo_data = 0, lo_witness = 0x0}, mtx_lock = 6}

16908288 = 0x1020000 (CLASS=1|LO_WITNESS)

While everything "looks" normal, mtx_lock = MTX_UNOWNED|MTX_CONTESTED

And kern_mutex.c cannot deal with that.

This is 100% repeatable/reproducible ...

Am I dealing with a VM bug or a FreeBSD bug?

Darren