zfs/syncer LOR

All,

I didn't see this LOR reported here:

http://sources.zabbadoz.net/freebsd/lor.html

Or with a quick perusal of the current_at_ archives, so apologies if it's
a known one.

I unfortunately don't recall what I was doing when this one popped up,
but if I can reproduce it, I'll certainly post some additional info.

Anyway, here it is:

lock order reversal:
 1st 0xffffff000b219ba8 zfs (zfs) _at_ /usr/src/sys/kern/vfs_mount.c:1193
 2nd 0xffffff000ba46270 syncer (syncer) _at_ /usr/src/sys/kern/vfs_subr.c:2206
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2a
_witness_debugger() at _witness_debugger+0x49
witness_checkorder() at witness_checkorder+0x7ca
__lockmgr_args() at __lockmgr_args+0xc2b
vop_stdlock() at vop_stdlock+0x39
VOP_LOCK1_APV() at VOP_LOCK1_APV+0x9b
_vn_lock() at _vn_lock+0x50
vrele() at vrele+0x121
dounmount() at dounmount+0x26a
unmount() at unmount+0x248
syscall() at syscall+0x1c1
Xfast_syscall() at Xfast_syscall+0xd0
--- syscall (22, FreeBSD ELF64, unmount), rip = 0x800695ecc, rsp =
0x7fffffffe298, rbp = 0x1 ---

Thanks,
Josh