LOR in dirhash

[Robert Schulze]

We are currently having continuous problems with 8-STABLE.
Since we upgraded, we have "double faults" every three days or so, 
yesterday we built a debugging kernel to identify the problem.

Today I saw a LOR in /var/log/messages, the whole output:

8<----------------------------------------------------------

lock order reversal:
1st 0xffffff81ef08ce98 bufwait (bufwait) @ /usr/src/sys/kern/vfs_bio.c:2636
2nd 0xffffff00157b4600 dirhash (dirhash) @ 
/usr/src/sys/ufs/ufs/ufs_dirhash.c:285
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2a
kdb_backtrace() at kdb_backtrace+0x37
_witness_debugger() at _witness_debugger+0x49
witness_checkorder() at witness_checkorder+0x7d3
_sx_xlock() at _sx_xlock+0x4a
ufsdirhash_acquire() at ufsdirhash_acquire+0x3a
ufsdirhash_add() at
ufsdirhash_add+0x19
ufs_diren
ter() at
ufs_direnter+0x876
ufs_makeinode() at
ufs_makeinode+0x239
VOP_CREATE_APV() at
VOP_CREATE_APV+0xb6
vn_open_cred() at vn_open_cred+0x415
kern_openat() at
kern_openat+0x165
syscallenter() at syscallenter+0xe5
syscall() at
syscall+0x55
Xfast_syscall() at
Xfast_syscall+0xe2
--- syscall (5, FreeBSD ELF64
, open)
, rip =
0x8009
a4a7c,
rsp = 0x
7ffffff
e918, r
bp = 0x1 ---

8<----------------------------------------------------------

maybe this is a seriuos one?

with kind regards,
Robert Schulze