6-current: udf broken, "locking against myself"

Further testing 6-current.  Seems like the udf filesystem is hosed, I
cannot even use a minimal one.

Mounting a udf (data) filesystem works, but the first attempt to use it
results in
"panic: lockmgr: locking against myself".

I put an minimal testing image on:
http://wavehh.dyndns.org/tmp/ll.udf.gz

It has been created with `mkisofs -udf dir` # no other options to mkisofs

Reproduce error:
$ mdconfig -a -t vnode -f ll.udf
md4
$ mount_udf /dev/md4 /mnt/tmp                   # works
$ cd /mnt/tmp                                   # still works
$ ls                                            # panic

This is a single-processor i386 machine with a single-processor
kernel.  Info on this machine (dmesg, pciconf, kernel config etc.) is
on http://www.cons.org/cracauer/machines/grisu/

A quick check on a 2-processor box with SMP support shows the same
panic.

Here are the symboled parts of the backtrace:
#23 0xc05888e0 in kdb_enter (msg=0x0) at cpufunc.h:60
#24 0xc056a4f5 in panic (fmt=0xc077896e "lockmgr: locking against myself")
    at ../../../kern/kern_shutdown.c:537
#25 0xc055baad in lockmgr (lkp=0xc2e27168, flags=12290, interlkp=0x80, 
    td=0xc2d6b600) at ../../../kern/kern_lock.c:329
#26 0xc05ca1cf in vop_stdlock (ap=0x0) at ../../../kern/vfs_default.c:258
#27 0xc074e364 in VOP_LOCK_APV (vop=0xc07b7500, a=0xf7cd8994)
    at vnode_if.c:1642
#28 0xc05e481c in vn_lock (vp=0xc2e27110, flags=4098, td=0xc2d6b600)
    at vnode_if.h:844
[addresses without symbols]
#56 0xc074d40e in VOP_CACHEDLOOKUP_APV (vop=0x0, a=0x0) at vnode_if.c:150

vnode_if.c:1642 is generated, it looks like this in this kernel (line
marked in # comment).

int
VOP_LOCK_APV(struct vop_vector *vop, struct vop_lock_args *a)
{
        int rc;

        VNASSERT(a->a_gen.a_desc == &vop_lock_desc, a->a_vp,
            ("Wrong a_desc in vop_lock(%p, %p)", a->a_vp, a));
        while(vop != NULL && \
            vop->vop_lock == NULL && vop->vop_bypass == NULL)
                vop = vop->vop_default;
        VNASSERT(vop != NULL, a->a_vp, ("No vop_lock(%p, %p)", a->a_vp, a));
        vop_lock_pre(a);
        if (vop->vop_lock != NULL)
                rc = vop->vop_lock(a); # this is the panic line 1642
        else
                rc = vop->vop_bypass(&a->a_gen);
        CTR3(KTR_VOP,
            "VOP_LOCK(vp 0x%lX, flags %ld, td 0x%lX)",
            a->a_vp, a->a_flags, a->a_td);
        if (rc == 0) {
        } else {
        }
        vop_lock_post(a, rc);
        return (rc);
}

Now, since I don't have anything useful in the backtrace, how do I go
about debugging an error like this?

Martin
-- 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Martin Cracauer <cracauer_at_cons.org>   http://www.cons.org/cracauer/
 No warranty.    This email is probably produced by one of my cats 
 stepping on the keys. No, I don't have an infinite number of cats.