UFS/VFS lock order reversal on stock 8.0-200812-AMD64

I'm new, so please advise me (gently?) about list protocol and such if needed.

Using stock 8.0-CURRENT-200812-amd64, I am getting the messages below.
I've run memtest 3.4 through 3 passes with no errors.
I did go through an entire boot/install with no errors by setting all caching to Write-Through in BIOS, but that leads to unacceptable performance, and I'm not sure the slowness wasn't masking the problem.
Motherboard is a Supermicro x7dvl3, 8G of RAM (4 x 2G matched within a small range of serial numbers.)
Chipset is an Intel 5000V with a ESB2 Southbridge. Cpu is 2 Quad core Xeon 5400 Series _at_ 2GHz. This is a fairly new CPU with a larger cache than previous Xeons (12Meg L2).
The error occurs whether I use the LSI 1068E attached via PCI-E(x4) or the ESB2 onboard SATA.
I do not get the error when mounting another drive after booting, I do see the same error when shutting down.
I also notice (maybe related) text video corruption during shutdown. (XGI Volari™ Z7 PCI-E Graphics Processor)

Am I too wordy, or did I forget something?


Trying to mount root from ufs:/dev/ad20s1a
lock order reversal:
 1st 0xffffff0001701070 user map (user map) _at_ /usr/src/sys/vm/vm_map.c:3115
 2nd 0xffffff0001ea87f8 ufs (ufs) _at_ /usr/src/sys/kern/vfs_subr.c:2079
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2a
_witness_debugger() at _witness_debugger+0x2e
witness_checkorder() at witness_checkorder+0x81e
__lockmgr_args() at __lockmgr_args+0xca8
ffs_lock() at ffs_lock+0x8c
VOP_LOCK1_APV() at VOP_LOCK1_APV+0x9b
_vn_lock() at _vn_lock+0x47
vget() at vget+0x8b
vnode_pager_lock() at vnode_pager_lock+0x1d0
vm_fault() at vm_fault+0x1e2
trap_pfault() at trap_pfault+0x128
trap() at trap+0x51c
calltrap() at calltrap+0x8
--- trap 0xc, rip = 0x40014f, rsp = 0x7fffffffee70, rbp = 0x7fffffffee90 ---

Later in the boot sequence
lock order reversal:
 1st 0xfffffffec0491330 bufwait (bufwait) _at_ /usr/src/sys/kern/vfs_bio.c:2443
 2nd 0xffffff0004163000 dirhash (dirhash) _at_ /usr/src/sys/ufs/ufs/ufs_dirhash.c:263
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2a
_witness_debugger() at _witness_debugger+0x2e
witness_checkorder() at witness_checkorder+0x81e
_sx_xlock() at _sx_xlock+0x55
ufsdirhash_acquire() at ufsdirhash_acquire+0x33
ufsdirhash_add() at ufsdirhash_add+0x19
ufs_direnter() at ufs_direnter+0x889
ufs_makeinode() at ufs_makeinode+0x338
VOP_CREATE_APV() at VOP_CREATE_APV+0x8d
vn_open_cred() at vn_open_cred+0x479
kern_openat() at kern_openat+0x169
syscall() at syscall+0x1bf
Xfast_syscall() at Xfast_syscall+0xab
--- syscall (5, FreeBSD ELF64, open), rip = 0x800daceac, rsp = 0x7fffffffe7c8, rbp = 0x8 ---

Thanks
Paul