KDB stack backtrace - i386 on boot

I get the following KDB stack backtraces each time I boot,
and occasionally afterwards. How can I interpret this info?

many thanks
anton

#dmesg
Copyright (c) 1992-2008 The FreeBSD Project.
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	The Regents of the University of California. All rights reserved.
FreeBSD is a registered trademark of The FreeBSD Foundation.
FreeBSD 8.0-CURRENT #0: Fri Sep 26 15:48:12 BST 2008
    mexas_at_mech-Anton240.men.bris.ac.uk:/usr/obj/usr/src/sys/EDGE
WARNING: WITNESS option enabled, expect reduced performance.
Timecounter "i8254" frequency 1193182 Hz quality 0
CPU: Intel(R) Pentium(R) 4 CPU 2.40GHz (2400.10-MHz 686-class CPU)
  Origin = "GenuineIntel"  Id = 0xf27  Stepping = 7
  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=0x400<CNXT-ID>
real memory  = 527695872 (503 MB)
avail memory = 507293696 (483 MB)
acpi0: <INTEL D845GRG2> on motherboard
acpi0: [ITHREAD]
acpi0: Power Button (fixed)
acpi0: reservation of 0, a0000 (3) failed
acpi0: reservation of 100000, 1f700000 (3) failed
Timecounter "ACPI-fast" frequency 3579545 Hz quality 1000
acpi_timer0: <24-bit timer at 3.579545MHz> port 0x408-0x40b on acpi0
pcib0: <ACPI Host-PCI bridge> port 0xcf8-0xcff on acpi0
pci0: <ACPI PCI bus> on pcib0
vgapci0: <VGA-compatible display> mem 0xf0000000-0xf7ffffff,0xffa80000-0xffafffff irq 11 at device 2.0 on pci0
agp0: <Intel 82845M (845M GMCH) SVGA controller> on vgapci0
agp0: detected 8060k stolen memory
agp0: aperture size is 128M
uhci0: <Intel 82801DB (ICH4) USB controller USB-A> port 0xe800-0xe81f irq 11 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 0xe880-0xe89f irq 3 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 0xec00-0xec1f irq 5 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 0xffa7fc00-0xffa7ffff irq 9 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
pcib1: <ACPI PCI-PCI bridge> at device 30.0 on pci0
pci1: <ACPI PCI bus> on pcib1
ahc0: <Adaptec 2940 Ultra SCSI adapter> port 0xd800-0xd8ff mem 0xff8ff000-0xff8fffff irq 10 at device 0.0 on pci1
ahc0: [ITHREAD]
aic7880: Ultra Wide Channel A, SCSI Id=7, 16/253 SCBs
fxp0: <Intel 82801DB (ICH4) Pro/100 VE Ethernet> port 0xdc00-0xdc3f mem 0xff8fe000-0xff8fefff irq 11 at device 8.0 on pci1
miibus0: <MII bus> on fxp0
inphy0: <i82562ET 10/100 media interface> PHY 1 on miibus0
inphy0:  10baseT, 10baseT-FDX, 100baseTX, 100baseTX-FDX, auto
fxp0: XXX: driver didn't set ifq_maxlen
fxp0: Ethernet address: 00:07:e9:e7:41:dc
fxp0: [ITHREAD]
isab0: <PCI-ISA bridge> at device 31.0 on pci0
isa0: <ISA bus> on isab0
atapci0: <Intel ICH4 UDMA100 controller> port 0x1f0-0x1f7,0x3f6,0x170-0x177,0x376,0xffa0-0xffaf at device 31.1 on pci0
ata0: <ATA channel 0> on atapci0
ata0: [ITHREAD]
ata1: <ATA channel 1> on atapci0
ata1: [ITHREAD]
pci0: <serial bus, SMBus> at device 31.3 (no driver attached)
pci0: <multimedia, audio> at device 31.5 (no driver attached)
acpi_button0: <Sleep Button> on acpi0
atrtc0: <AT realtime clock> port 0x70-0x71 irq 8 on acpi0
fdc0: <floppy drive controller> port 0x3f0-0x3f1,0x3f2-0x3f3,0x3f4-0x3f5,0x3f7 irq 6 drq 2 on acpi0
fdc0: [FILTER]
fd0: <1440-KB 3.5" drive> on fdc0 drive 0
uart0: <16550 or compatible> port 0x3f8-0x3ff irq 4 flags 0x10 on acpi0
uart0: [FILTER]
ppc0: <Parallel port> port 0x378-0x37f,0x778-0x77f irq 7 drq 3 on acpi0
ppc0: SMC-like chipset (ECP/EPP/PS2/NIBBLE) in COMPATIBLE mode
ppc0: FIFO with 16/16/8 bytes threshold
ppc0: [GIANT-LOCKED]
ppc0: [ITHREAD]
ppbus0: <Parallel port bus> on ppc0
plip0: <PLIP network interface> on ppbus0
plip0: WARNING: using obsoleted IFF_NEEDSGIANT flag
lpt0: <Printer> on ppbus0
lpt0: Interrupt-driven port
ppi0: <Parallel I/O> on ppbus0
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
pmtimer0 on isa0
orm0: <ISA Option ROM> at iomem 0xcb800-0xcbfff pnpid ORM0000 on isa0
vga0: <Generic ISA VGA> at port 0x3c0-0x3df iomem 0xa0000-0xbffff on isa0
sc0: <System console> at flags 0x100 on isa0
sc0: VGA <16 virtual consoles, flags=0x300>
Timecounter "TSC" frequency 2400096344 Hz quality 800
Timecounters tick every 1.000 msec
Waiting 5 seconds for SCSI devices to settle
ad0: 76319MB <WDC WD800BB-00CAA1 17.07W17> at ata0-master UDMA100
acd0: DVDROM <DVD-ROM DDU1621/VER S2.9> at ata1-master UDMA33
acd1: CDRW <SONY CD-RW CRX210E1/2YS2> at ata1-slave UDMA33
WARNING: WITNESS option enabled, expect reduced performance.
Trying to mount root from ufs:/dev/ad0s1a
lock order reversal:
 1st 0xc2f17000 vfslock (vfslock) _at_ /usr/src/sys/kern/vfs_subr.c:372
 2nd 0xc2e69df4 devfs (devfs) _at_ /usr/src/sys/kern/vfs_lookup.c:432
 3rd 0xc2f16d34 vfslock (vfslock) _at_ /usr/src/sys/kern/vfs_subr.c:372
KDB: stack backtrace:
db_trace_self_wrapper(c07f0d22,c2a11820,c05f8069,4,c07ec87d,...) at db_trace_self_wrapper+0x26
kdb_backtrace(4,c07ec87d,c09b2800,c2c2d960,c2a11878,...) at kdb_backtrace+0x29
_witness_debugger(c07f340c,c2f16d34,c07f9d2e,c2c2d960,c07fa2d3,...) at _witness_debugger+0x21
witness_checkorder(c2f16d34,1,c07fa2d3,174,0,...) at witness_checkorder+0x7db
__lockmgr_args(c2f16d34,200100,c2f16d50,0,0,...) at __lockmgr_args+0x226
vfs_busy(c2f16d34,200,0,c2e69e10,c0855380,...) at vfs_busy+0x1b2
vfs_mount_alloc(c2e69d9c,c0855380,c2f00240,c2c48d00,0,...) at vfs_mount_alloc+0x74
vfs_donmount(c2c69d20,4001,c2a11b50,c2eff500,6,...) at vfs_donmount+0x126e
kernel_mount(c2e07a90,4001,c2f0cd80,ffffffff,c2a11bc0) at kernel_mount+0x78
kernel_vmount(4001,c07f9f1d,c2f00250,c07f9f2c,c07e745e,...) at kernel_vmount+0x61
vfs_mountroot_try(c07fa22f,c07e745e,c07e1c45,1,c0635b67,...) at vfs_mountroot_try+0x12c
vfs_mountroot(c087f270,4,c07e87e0,265,6b3fedcf,...) at vfs_mountroot+0x3f7
start_init(0,c2a11d38,c07ea1b2,322,c2c66d0c,...) at start_init+0x65
fork_exit(c0587dc5,0,c2a11d38) at fork_exit+0xb8
fork_trampoline() at fork_trampoline+0x8
--- trap 0, eip = 0, esp = 0xc2a11d70, ebp = 0 ---
lock order reversal:
 1st 0xc2e699c4 ufs (ufs) _at_ /usr/src/sys/kern/vfs_subr.c:2051
 2nd 0xc2f17000 vfslock (vfslock) _at_ /usr/src/sys/kern/vfs_subr.c:372
KDB: stack backtrace:
db_trace_self_wrapper(c07f0d22,c2a118f4,c05f8069,4,c07ec87d,...) at db_trace_self_wrapper+0x26
kdb_backtrace(4,c07ec87d,c09b24e8,c2c2d960,c2a1194c,...) at kdb_backtrace+0x29
_witness_debugger(c07f33f3,c2f17000,c07f9d2e,c2c2d960,c07fa2d3,...) at _witness_debugger+0x21
witness_checkorder(c2f17000,1,c07fa2d3,174,0,...) at witness_checkorder+0x7db
__lockmgr_args(c2f17000,200100,c2f1701c,0,0,...) at __lockmgr_args+0x226
vfs_busy(c2f17000,0,0,1b0,c2a11b24,...) at vfs_busy+0x1b2
lookup(c2a11b0c,c07f99de,d8,c0,c2c48e2c,...) at lookup+0x793
namei(c2a11b0c,c2a11b24,c05f7ed7,c2c69dc4,c07fa075,...) at namei+0x434
kern_unlinkat(c2c69d20,ffffff9c,c07fa075,1,c2a11c5c,...) at kern_unlinkat+0x3f
kern_unlink(c2c69d20,c07fa075,1,631,0,...) at kern_unlink+0x27
vfs_mountroot_try(c07fa22f,c07e745e,c07e1c45,1,c0635b67,...) at vfs_mountroot_try+0x469
vfs_mountroot(c087f270,4,c07e87e0,265,6b3fedcf,...) at vfs_mountroot+0x3f7
start_init(0,c2a11d38,c07ea1b2,322,c2c66d0c,...) at start_init+0x65
fork_exit(c0587dc5,0,c2a11d38) at fork_exit+0xb8
fork_trampoline() at fork_trampoline+0x8
--- trap 0, eip = 0, esp = 0xc2a11d70, ebp = 0 ---
lock order reversal:
 1st 0xc2c6c044 user map (user map) _at_ /usr/src/sys/vm/vm_map.c:3115
 2nd 0xc2e697ac ufs (ufs) _at_ /usr/src/sys/kern/vfs_subr.c:2051
KDB: stack backtrace:
db_trace_self_wrapper(c07f0d22,c2a11918,c05f8069,4,c07ec87d,...) at db_trace_self_wrapper+0x26
kdb_backtrace(4,c07ec87d,c09b24e8,c2c2dbd0,c2a11970,...) at kdb_backtrace+0x29
_witness_debugger(c07f33f3,c2e697ac,c07e7d55,c2c2dbd0,c07fa2d3,...) at _witness_debugger+0x21
witness_checkorder(c2e697ac,1,c07fa2d3,803,0,...) at witness_checkorder+0x7db
__lockmgr_args(c2e697ac,200501,c2e697c8,0,0,...) at __lockmgr_args+0x226
ffs_lock(c2a11a7c,c080cff1,c07e745c,200501,c2e69754,...) at ffs_lock+0x7d
VOP_LOCK1_APV(c0855740,c2a11a7c,c0865c20,c2e69754,200501,...) at VOP_LOCK1_APV+0xab
_vn_lock(c2e69754,200501,c07fa2d3,803,4,...) at _vn_lock+0x5e
vget(c2e69754,200501,c2c69d20,4b4,0,...) at vget+0xc1
vnode_pager_lock(c10452e8,0,c080a5b3,127,c2a11c18,...) at vnode_pager_lock+0x1d3
vm_fault(c2c6c000,80d6000,2,8,80d68a0,...) at vm_fault+0x1e8
trap_pfault(5,0,c0815460,2f5,c,...) at trap_pfault+0xf9
trap(c2a11d38) at trap+0x265
calltrap() at calltrap+0x6
--- trap 0xc, eip = 0x80480e5, esp = 0xbfbfeef0, ebp = 0xbfbfef10 ---

-- 
Anton Shterenlikht
Room 2.6, Queen's Building
Mech Eng Dept
Bristol University
University Walk, Bristol BS8 1TR, UK
Tel: +44 (0)117 928 8233 
Fax: +44 (0)117 929 4423