page fault panic in knote

This happened on shutdown, I think I magially hit enter twice
when I fired off the shutdown command. This is on RELENG_5 from
2004-10-11. The system was also running in single-user at the time
so no crash dump.

-- serial snip --
# sync
# sync
# shutdown -r now
Shutdown NOW!
shutdown: [pid 1183]
Oct 11 22:06:07 shutdown: reboot by root:
#
System shutdown time has arrived

Fatal trap 12: page fault while in kernel mode
cpuid = 0; apic id = 00
fault virtual address   = 0x1c
fault code              = supervisor write, page not present
instruction pointer     = 0x8:0xc04a88da
stack pointer           = 0x10:0xd4265728
frame pointer           = 0x10:0xd4265748
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         = 1 (init)
[thread 100002]
Stopped at      knote+0x2a:     lock cmpxchgl   %ecx,0x1c(%edx)
db> tr
knote(c17a1898,0,0) at knote+0x2a
ttwwakeup(c17a1800,0,c1561320,0,ffffffff) at ttwwakeup+0xee
comstart(c17a1800,2580,0,0,c) at comstart+0x41e
comparam(c17a1800,c17a18a4,0,c17c0420,c1561320) at comparam+0x28b
sioopen(c06940c0,6,2000,c1561320,c0488928) at sioopen+0x216
spec_open(d4265860,d426591c,c0541a8e,d4265860,a) at spec_open+0x34a
spec_vnoperate(d4265860,a,20010002,80,c1561320) at spec_vnoperate+0x18
vn_open_cred(d4265960,c069cfb8,0,c155e480,ffffffff) at vn_open_cred+0x45e
vn_open(d4265960,c069cfb8,0,ffffffff,c17c0a50) at vn_open+0x33
cn_devopen(c069cf80,c1561320,0,0,6) at cn_devopen+0xe9
cnopen(c0692f88,6,2000,c1561320,c1561320) at cnopen+0x54
spec_open(d4265a70,d4265b2c,c0541a8e,d4265a70,c17cf000) at spec_open+0x34a
spec_vnoperate(d4265a70,c17cf000,0,80,c1561320) at spec_vnoperate+0x18
vn_open_cred(d4265bd8,d4265cd8,0,c155e480,0) at vn_open_cred+0x45e
vn_open(d4265bd8,d4265cd8,0,0,0) at vn_open+0x33
kern_open(c1561320,80b5aa2,0,6,0) at kern_open+0x113
open(c1561320,d4265d14,c,c1561320,7) at open+0x30
syscall(2f,2f,2f,80dc5e0,bfbfe4b0) at syscall+0x330
Xint0x80_syscall() at Xint0x80_syscall+0x1f
--- syscall (5, FreeBSD ELF32, open), eip = 0x80534a7, esp = 0xbfbfe02c, ebp = 
0xbfbfecc8 ---
db> panic
panic: from debugger
cpuid = 0
Uptime: 19m21s
Cannot dump. No dump device defined.
Shutting down ACPI
Automatic reboot in 15 seconds - press a key on the console to abort
Rebooting...

-- 
Pawel