Witness message about lock order reversal on 10 (head)

I got these messages on 10 head, rev.254235, during 'filesystem full' condition.

Yuri


===== log =====
lock order reversal:
  1st 0xffffff80f7432470 bufwait (bufwait) _at_ /usr/src/sys/kern/vfs_bio.c:3054
  2nd 0xfffffe00075b5600 dirhash (dirhash) _at_ /usr/src/sys/ufs/ufs/ufs_dirhash.c:284
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xffffff8000284440
kdb_backtrace() at kdb_backtrace+0x39/frame 0xffffff80002844f0
witness_checkorder() at witness_checkorder+0xd4f/frame 0xffffff8000284580
_sx_xlock() at _sx_xlock+0x75/frame 0xffffff80002845c0
ufsdirhash_add() at ufsdirhash_add+0x3b/frame 0xffffff8000284600
ufs_direnter() at ufs_direnter+0x688/frame 0xffffff80002846c0
ufs_mkdir() at ufs_mkdir+0x863/frame 0xffffff80002848c0
VOP_MKDIR_APV() at VOP_MKDIR_APV+0xf0/frame 0xffffff80002848f0
kern_mkdirat() at kern_mkdirat+0x21a/frame 0xffffff8000284ae0
amd64_syscall() at amd64_syscall+0x265/frame 0xffffff8000284bf0
Xfast_syscall() at Xfast_syscall+0xfb/frame 0xffffff8000284bf0
--- syscall (136, FreeBSD ELF64, sys_mkdir), rip = 0x800931e9a, rsp = 0x7fffffffd798, rbp = 0x7fffffffdc70 ---
lock order reversal:
  1st 0xfffffe0007633840 filedesc structure (filedesc structure) _at_ /usr/src/sys/kern/kern_descrip.c:1184
  2nd 0xfffffe0007a45240 ufs (ufs) _at_ /usr/src/sys/kern/vfs_subr.c:4346
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xffffff800031f6b0
kdb_backtrace() at kdb_backtrace+0x39/frame 0xffffff800031f760
witness_checkorder() at witness_checkorder+0xd4f/frame 0xffffff800031f7f0
__lockmgr_args() at __lockmgr_args+0x6f2/frame 0xffffff800031f920
ffs_lock() at ffs_lock+0x84/frame 0xffffff800031f970
VOP_LOCK1_APV() at VOP_LOCK1_APV+0xf5/frame 0xffffff800031f9a0
_vn_lock() at _vn_lock+0xab/frame 0xffffff800031fa10
knlist_remove_kq() at knlist_remove_kq+0x82/frame 0xffffff800031fa40
knote_fdclose() at knote_fdclose+0xc8/frame 0xffffff800031fa90
closefp() at closefp+0x64/frame 0xffffff800031fae0
amd64_syscall() at amd64_syscall+0x265/frame 0xffffff800031fbf0
Xfast_syscall() at Xfast_syscall+0xfb/frame 0xffffff800031fbf0
--- syscall (6, FreeBSD ELF64, sys_close), rip = 0x80164537a, rsp = 0x7fffff7fbf08, rbp = 0x7fffff7fbf20 ---
pid 983 (sendmail), uid 25 inumber 473785 on /: filesystem full
pid 1101 (dd), uid 2 inumber 426338 on /: filesystem full
lock order reversal:
  1st 0xfffffe0007cbc240 ufs (ufs) _at_ /usr/src/sys/kern/vfs_subr.c:2099
  2nd 0xffffff80f7894338 bufwait (bufwait) _at_ /usr/src/sys/ufs/ffs/ffs_vnops.c:262
  3rd 0xfffffe003b531418 ufs (ufs) _at_ /usr/src/sys/kern/vfs_subr.c:2099
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xffffff8000378e60
kdb_backtrace() at kdb_backtrace+0x39/frame 0xffffff8000378f10
witness_checkorder() at witness_checkorder+0xd4f/frame 0xffffff8000378fa0
__lockmgr_args() at __lockmgr_args+0x6f2/frame 0xffffff80003790d0
ffs_lock() at ffs_lock+0x84/frame 0xffffff8000379120
VOP_LOCK1_APV() at VOP_LOCK1_APV+0xf5/frame 0xffffff8000379150
_vn_lock() at _vn_lock+0xab/frame 0xffffff80003791c0
vget() at vget+0x70/frame 0xffffff8000379210
vfs_hash_get() at vfs_hash_get+0xf5/frame 0xffffff8000379260
ffs_vgetf() at ffs_vgetf+0x41/frame 0xffffff80003792f0
softdep_sync_buf() at softdep_sync_buf+0x2e4/frame 0xffffff80003793a0
ffs_syncvnode() at ffs_syncvnode+0x258/frame 0xffffff8000379420
ffs_truncate() at ffs_truncate+0x5ca/frame 0xffffff8000379600
ufs_direnter() at ufs_direnter+0x891/frame 0xffffff80003796c0
ufs_mkdir() at ufs_mkdir+0x863/frame 0xffffff80003798c0
VOP_MKDIR_APV() at VOP_MKDIR_APV+0xf0/frame 0xffffff80003798f0
kern_mkdirat() at kern_mkdirat+0x21a/frame 0xffffff8000379ae0
amd64_syscall() at amd64_syscall+0x265/frame 0xffffff8000379bf0
Xfast_syscall() at Xfast_syscall+0xfb/frame 0xffffff8000379bf0
--- syscall (136, FreeBSD ELF64, sys_mkdir), rip = 0x800931e9a, rsp = 0x7fffffffd898, rbp = 0x7fffffffd970 ---