pfctl -f causes fatal trap 12

On a recent -CURRENT kernel (Sat Feb 12 01:37:39 EST 2005)

pf is compiled into the kernel, booted single user:

# cd /usr/src/sbin/pfctl
# ./pfctl -e
pf enabled
# ./pfctl -f /etc/pf.conf


Fatal trap 12: page fault while in kernel mode
fault virtual address	= 0x0
fault code		= supervisor read, page not present
instruction pointer	= 0x8:0xc0615540
stack pointer	        = 0x10:0xcbca2ca8
frame pointer	        = 0x10:0xcbca2cb4
code segment		= base 0x0, limit 0xfffff, type 0x1b
			= DPL 0, pres 1, def32 1, gran 1
processor eflags	= interrupt enabled, resume, IOPL = 0
current process		= 27 (swi4: clock sio)
[thread pid 27 tid 100001 ]
Stopped at      _mtx_unlock_flags+0x34: cmpl    $0xc08a13a8,0(%ebx)

From kgdb:
(kgdb) where
...
#11 0xc0627fdc in softclock (dummy=0x0) at /usr/src/sys/kern/kern_timeout.c:315
#12 0xc060b324 in ithread_loop (arg=0xc14fc500)
    at /usr/src/sys/kern/kern_intr.c:546
#13 0xc060a7b4 in fork_exit (callout=0xc060b204 <ithread_loop>,
    arg=0xc14fc500, frame=0xcbca2d48) at /usr/src/sys/kern/kern_fork.c:790
#14 0xc07cb02c in fork_trampoline () at /usr/src/sys/i386/i386/exception.s:208
(kgdb) frame 11
#11 0xc0627fdc in softclock (dummy=0x0) at /usr/src/sys/kern/kern_timeout.c:315
315                                             mtx_unlock(c_mtx);
(kgdb) print c_mtx
$1 = (struct mtx *) 0x0
(kgdb) up
#12 0xc060b324 in ithread_loop (arg=0xc14fc500)
    at /usr/src/sys/kern/kern_intr.c:546
546                                     ih->ih_handler(ih->ih_argument);
(kgdb)