lor freebsd zfs mount

[Marcin Cieslak]

r203753, amd64, while booting (mount filesystems)::

lock order reversal:
  1st 0xffffff00096c4098 zfs (zfs) @ /usr/src/sys/kern/vfs_mount.c:1058
  2nd 0xffffff000973f9f8 devfs (devfs) @ /usr/src/sys/kern/vfs_subr.c:2091
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2a
_witness_debugger() at _witness_debugger+0x49
witness_checkorder() at witness_checkorder+0x7ea
__lockmgr_args() at __lockmgr_args+0xd43
vop_stdlock() at vop_stdlock+0x39
VOP_LOCK1_APV() at VOP_LOCK1_APV+0x9b
_vn_lock() at _vn_lock+0x50
vget() at vget+0x6e
devfs_allocv() at devfs_allocv+0xee
devfs_root() at devfs_root+0x41
vfs_donmount() at vfs_donmount+0xfa8
nmount() at nmount+0x74
syscall() at syscall+0x102
Xfast_syscall() at Xfast_syscall+0xe1
--- syscall (378, FreeBSD ELF64, nmount), rip = 0x8007ac37c, rsp = 0x7fffffffdd28, rbp = 0x800a06048 ---

--Marcin