Fatal trap 12: page fault while in kernel mode

Hi,

I found that my 8-current box sometimes gets panic recently.
>From a serial console, I saved a textdump.

Fatal trap 12: page fault while in kernel mode
cpuid = 0; apic id = 00
fault virtual address   = 0x0
fault code              = supervisor read, page not present
instruction pointer     = 0x20:0xc0a57285
stack pointer           = 0x28:0xe682dc44
frame pointer           = 0x28:0xe682dcec
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         = 1015 (nfsd: service)
panic: from debugger
cpuid = 0
KDB: stack backtrace:
Uptime: 1d16h10m24s

And,

$ addr2line -e /boot/kernel/kernel.symbols 0xc0a57285
/usr/src/sys/rpc/svc.c:787

    781         /* now receive msgs from xprtprt (support batch calls) */
    782         r = malloc(sizeof(*r), M_RPC, M_WAITOK|M_ZERO);
    783
    784         msg.rm_call.cb_cred.oa_base = r->rq_credarea;
    785         msg.rm_call.cb_verf.oa_base = &r->rq_credarea[MAX_AUTH_BYTES];
    786         r->rq_clntcred = &r->rq_credarea[2*MAX_AUTH_BYTES];
    787         if (SVC_RECV(xprt, &msg, &r->rq_addr, &args)) {
    788                 enum auth_stat why;
    789

Why this occurs and what do I have to check?

=== /var/run/dmesg.boot ===
Copyright (c) 1992-2008 The FreeBSD Project.
Copyright (c) 1979, 1980, 1983, 1986, 1988, 1989, 1991, 1992, 1993, 1994
	The Regents of the University of California. All rights reserved.
FreeBSD is a registered trademark of The FreeBSD Foundation.
FreeBSD 8.0-CURRENT #167: Wed Dec  3 11:33:19 JST 2008
    root_at_roddy.4407.kankyo-u.ac.jp:/usr/obj/usr/src/sys/RODDY
Timecounter "i8254" frequency 1193182 Hz quality 0
CPU: Intel(R) Xeon(TM) CPU 2.40GHz (2392.04-MHz 686-class CPU)
  Origin = "GenuineIntel"  Id = 0xf25  Stepping = 5
  Features=0xbfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,DTS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE>
  Features2=0x4400<CNXT-ID,xTPR>
  Logical CPUs per core: 2
real memory  = 1073152000 (1023 MB)
avail memory = 1036349440 (988 MB)
ACPI APIC Table: <PTLTD  	 APIC  >
FreeBSD/SMP: Multiprocessor System Detected: 4 CPUs
 cpu0 (BSP): APIC ID:  0
 cpu1 (AP): APIC ID:  1
 cpu2 (AP): APIC ID:  6
 cpu3 (AP): APIC ID:  7
ioapic0 <Version 2.0> irqs 0-23 on motherboard
ioapic1 <Version 2.0> irqs 24-47 on motherboard
ioapic2 <Version 2.0> irqs 48-71 on motherboard
kbd1 at kbdmux0
acpi0: <PTLTD   RSDT> on motherboard
acpi0: [ITHREAD]
acpi0: Power Button (fixed)
can't fetch resources for \\_SB_.PCI0.LPC0.SIO_.LPT_ - AE_AML_INVALID_RESOURCE_TYPE
Timecounter "ACPI-fast" frequency 3579545 Hz quality 1000
acpi_timer0: <24-bit timer at 3.579545MHz> port 0x1008-0x100b on acpi0
pcib0: <ACPI Host-PCI bridge> port 0xcf8-0xcff on acpi0
pci0: <ACPI PCI bus> on pcib0
agp0: <Intel E7505 host to AGP bridge> on hostb0
pci0: <unknown> at device 0.1 (no driver attached)
pcib1: <ACPI PCI-PCI bridge> mem 0xf8000000-0xfbffffff at device 1.0 on pci0
pci1: <ACPI PCI bus> on pcib1
vgapci0: <VGA-compatible display> mem 0xfc000000-0xfdffffff,0xf0100000-0xf0103fff,0xf0800000-0xf0ffffff irq 16 at device 0.0 on pci1
drm0: <Matrox G550 (AGP)> on vgapci0
vgapci0: child drm0 requested pci_enable_busmaster
info: [drm] AGP at 0xf4000000 64MB
info: [drm] Initialized mga 3.2.2 20060319
pcib2: <ACPI PCI-PCI bridge> at device 2.0 on pci0
pci2: <ACPI PCI bus> on pcib2
pcib3: <ACPI PCI-PCI bridge> at device 29.0 on pci2
pci3: <ACPI PCI bus> on pcib3
pcib4: <ACPI PCI-PCI bridge> at device 31.0 on pci2
pci4: <ACPI PCI bus> on pcib4
bge0: <Broadcom NetXtreme Gigabit Ethernet Controller, ASIC rev. 0x1002> mem 0xf1100000-0xf110ffff irq 52 at device 4.0 on pci4
miibus0: <MII bus> on bge0
brgphy0: <BCM5703 10/100/1000baseTX PHY> PHY 1 on miibus0
brgphy0:  10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, 1000baseT, 1000baseT-FDX, auto
bge0: Ethernet address: 00:50:45:00:a0:37
bge0: [ITHREAD]
uhci0: <Intel 82801DB (ICH4) USB controller USB-A> port 0x1400-0x141f irq 16 at device 29.0 on pci0
uhci0: [GIANT-LOCKED]
uhci0: [ITHREAD]
usb0: <Intel 82801DB (ICH4) USB controller USB-A> on uhci0
usb0: USB revision 1.0
uhub0: <Intel UHCI root hub, class 9/0, rev 1.00/1.00, addr 1> on usb0
uhub0: 2 ports with 2 removable, self powered
uhci1: <Intel 82801DB (ICH4) USB controller USB-B> port 0x1420-0x143f irq 19 at device 29.1 on pci0
uhci1: [GIANT-LOCKED]
uhci1: [ITHREAD]
usb1: <Intel 82801DB (ICH4) USB controller USB-B> on uhci1
usb1: USB revision 1.0
uhub1: <Intel UHCI root hub, class 9/0, rev 1.00/1.00, addr 1> on usb1
uhub1: 2 ports with 2 removable, self powered
uhci2: <Intel 82801DB (ICH4) USB controller USB-C> port 0x1440-0x145f irq 18 at device 29.2 on pci0
uhci2: [GIANT-LOCKED]
uhci2: [ITHREAD]
usb2: <Intel 82801DB (ICH4) USB controller USB-C> on uhci2
usb2: USB revision 1.0
uhub2: <Intel UHCI root hub, class 9/0, rev 1.00/1.00, addr 1> on usb2
uhub2: 2 ports with 2 removable, self powered
ehci0: <Intel 82801DB/L/M (ICH4) USB 2.0 controller> mem 0xf0000000-0xf00003ff irq 23 at device 29.7 on pci0
ehci0: [GIANT-LOCKED]
ehci0: [ITHREAD]
usb3: EHCI version 1.0
usb3: companion controllers, 2 ports each: usb0 usb1 usb2
usb3: <Intel 82801DB/L/M (ICH4) USB 2.0 controller> on ehci0
usb3: USB revision 2.0
uhub3: <Intel EHCI root hub, class 9/0, rev 2.00/1.00, addr 1> on usb3
uhub3: 6 ports with 6 removable, self powered
pcib5: <ACPI PCI-PCI bridge> at device 30.0 on pci0
pci5: <ACPI PCI bus> on pcib5
atapci0: <HighPoint HPT370 UDMA100 controller> port 0x2450-0x2457,0x2444-0x2447,0x2448-0x244f,0x2440-0x2443,0x2000-0x20ff irq 21 at device 0.0 on pci5
atapci0: [ITHREAD]
ata2: <ATA channel 0> on atapci0
ata2: [ITHREAD]
ata3: <ATA channel 1> on atapci0
ata3: [ITHREAD]
pcm0: <Creative CT5880-C> port 0x2400-0x243f irq 22 at device 1.0 on pci5
pcm0: <SigmaTel STAC9708/11 AC97 Codec>
pcm0: [ITHREAD]
pcm0: <Playback: DAC1,DAC2 / Record: ADC>
isab0: <PCI-ISA bridge> at device 31.0 on pci0
isa0: <ISA bus> on isab0
atapci1: <Intel ICH4 UDMA100 controller> port 0x1f0-0x1f7,0x3f6,0x170-0x177,0x376,0x1460-0x146f at device 31.1 on pci0
ata0: <ATA channel 0> on atapci1
ata0: [ITHREAD]
ata1: <ATA channel 1> on atapci1
ata1: [ITHREAD]
pci0: <serial bus, SMBus> at device 31.3 (no driver attached)
acpi_button0: <Power Button> on acpi0
atrtc0: <AT realtime clock> port 0x70-0x71 irq 8 on acpi0
fdc0: <floppy drive controller> port 0x3f0-0x3f5,0x3f7 irq 6 drq 2 on acpi0
fdc0: [FILTER]
fd0: <1440-KB 3.5" drive> on fdc0 drive 0
ppc1: <Parallel port> port 0x378-0x37f on acpi0
ppc1: SMC-like chipset (ECP/EPP/PS2/NIBBLE) in COMPATIBLE mode
ppc1: FIFO with 16/16/8 bytes threshold
ppbus0: <Parallel port bus> on ppc1
ppbus0: IEEE1284 device found /NIBBLE/PS2
ppbus0: Probing for PnP devices:
ppbus0: <Canon LASER SHOT LBP-850> PRINTER LIPS,N201,ESCP,HP-GL,CJL
plip0: <PLIP network interface> on ppbus0
plip0: cannot reserve interrupt, failed.
device_attach: plip0 attach returned 6
lpt0: <Printer> on ppbus0
lpt0: Polled port
ppi0: <Parallel I/O> on ppbus0
uart1: <16550 or compatible> port 0x2f8-0x2ff irq 3 on acpi0
uart1: [FILTER]
uart0: <16550 or compatible> port 0x3f8-0x3ff irq 4 flags 0x30 on acpi0
uart0: [FILTER]
uart0: console (9600,n,8,1)
atkbdc0: <Keyboard controller (i8042)> port 0x60,0x64 irq 1 on acpi0
atkbd0: <AT Keyboard> irq 1 on atkbdc0
kbd0 at atkbd0
atkbd0: [GIANT-LOCKED]
atkbd0: [ITHREAD]
psm0: <PS/2 Mouse> irq 12 on atkbdc0
psm0: [GIANT-LOCKED]
psm0: [ITHREAD]
psm0: model IntelliMouse, device ID 3
cpu0: <ACPI CPU> on acpi0
p4tcc0: <CPU Frequency Thermal Control> on cpu0
cpu1: <ACPI CPU> on acpi0
p4tcc1: <CPU Frequency Thermal Control> on cpu1
pmtimer0 on isa0
orm0: <ISA Option ROMs> at iomem 0xc0000-0xc8fff,0xc9000-0xd4fff,0xe0000-0xe3fff pnpid ORM0000 on isa0
sc0: <System console> at flags 0x100 on isa0
sc0: VGA <16 virtual consoles, flags=0x300>
vga0: <Generic ISA VGA> at port 0x3c0-0x3df iomem 0xa0000-0xbffff on isa0
ppc0: parallel port not found.
uhid0: <OMRON BY75SW, class 0/0, rev 1.10/0.05, addr 2> on uhub1
Timecounters tick every 1.000 msec
ad0: 114473MB <Seagate ST3120022A 3.06> at ata0-master UDMA100
acd0: DVDR <TSSTcorpCD/DVDW TS-H652L/TI02> at ata1-master UDMA33
ad4: DMA limited to UDMA33, controller found non-ATA66 cable
ad4: 152627MB <ACCUSYS ACS7500 CDVL ACCUSYS> at ata2-master UDMA33
ad6: 152627MB <Hitachi HDS721616PLAT80 P22OA8BA> at ata3-master UDMA100
SMP: AP CPU #2 Launched!
SMP: AP CPU #1 Launched!
SMP: AP CPU #3 Launched!
Trying to mount root from ufs:/dev/ad0s1a
WARNING: / was not properly dismounted
umass0: <LOGITEC LHD-EDU2, class 0/0, rev 2.00/1.00, addr 2> on uhub3
da0 at umass-sim0 bus 0 target 0 lun 0
da0: <LOGITEC LHD-EDU2 6.11> Fixed Direct Access SCSI-0 device 
da0: 40.000MB/s transfers
da0: 286188MB (586114703 512 byte sectors: 255H 63S/T 36483C)

=== /sys/i386/conf/RODDY ===
include GENERIC

ident		RODDY

nooption	INVARIANTS
nooption	INVARIANT_SUPPORT
nooption	WITNESS
nooption	WITNESS_SKIPSPIN

device	sound
device	"snd_es137x"

options		MSGBUF_SIZE=81920

options		DEVICE_POLLING
options		HZ=1000

options		NETATALK
-- 
NAKAJI Hiroyuki