A March 1 kernel (1.3J, I think) dies with a uvm_fault when I try to
mount a unionfs... the problem seems to be that the code at vref+6 is
trying to dereference a null pointer. vref+6 is the first line of
vref(); vp is a null pointer:
        simple_lock(&vp->v_interlock);

I'm on NetBSD/i386, relevant lines of /etc/fstab are:
/dev/ccd0d /usr ffs rw 1 2
/usr/src /usr/src.local union rw,-b

-- 
Name: Dave Huang     |   Mammal, mammal / their names are called /
INet: khym@bga.com   |   they raise a paw / the bat, the cat /
FurryMUCK: Dahan     |   dolphin and dog / koala bear and hog -- TMBG
Dahan: Hani G Y+C 23 Y++ L+++ W- C++ T++ A+ E+ S++ V++ F- Q+++ P+ B+ PA+ PL++