acquiring duplicate lock of same type: "vnode interlock"

I got a witness message in my console with today's -current (not RELENG_5_2).


----- console
acquiring duplicate lock of same type: "vnode interlock"
 1st vnode interlock _at_ ufs/ffs/ffs_snapshot.c:1794
 2nd vnode interlock _at_ ufs/ffs/ffs_snapshot.c:1796
Stack backtrace:
backtrace(c0734d9b,c073959e,c0748dca,704,c82a0008) at backtrace+0x17
witness_lock(c864c6f0,8,c0748dca,704,c860bdac) at witness_lock+0x672
_mtx_lock_flags(c864c6f0,0,c0748dc1,704,c072bed0) at _mtx_lock_flags+0xba
ffs_snapshot_mount(c85b2800,c85b2800,c8599000,c42f1600,c42f1600) at ffs_snapshot_mount+0x2b0
ffs_mountfs(c864ccb8,c85b2800,c82a8000,c0557bd0,c07317d6) at ffs_mountfs+0xa6e
ffs_mount(c85b2800,c864b400,bfbfe1f0,e80bbbec,c82a8000) at ffs_mount+0x90f
vfs_domount(c82a8000,c85aa440,c864b400,0,bfbfe1f0) at vfs_domount+0x884
mount(c82a8000,e80bbd14,c0752787,3ee,4) at mount+0xc0
syscall(2f,2f,2f,804ad73,2) at syscall+0x2c0
Xint0x80_syscall() at Xint0x80_syscall+0x1d
--- syscall (21), eip = 0x280c0f2f, esp = 0xbfbfe1cc, ebp = 0xbfbfe268 ---


-- 
Jun Kuriyama <kuriyama_at_imgsrc.co.jp> // IMG SRC, Inc.
             <kuriyama_at_FreeBSD.org> // FreeBSD Project