gnop panic with recent kernel (r256923)

I get a "gnop lock" panic when trying to create a gnop device:

 	# gnop create -S 4k ada3

panic: lock "gnop lock" 0xfffff80002566640 already initialized


# kgdb /boot/kernel.r256923/kernel /var/crash/vmcore.last
...
Unread portion of the kernel message buffer:
panic: lock "gnop lock" 0xfffff80002566640 already initialized
cpuid = 1
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe00934f3830
kdb_backtrace() at kdb_backtrace+0x39/frame 0xfffffe00934f38e0
vpanic() at vpanic+0x126/frame 0xfffffe00934f3920
kassert_panic() at kassert_panic+0x136/frame 0xfffffe00934f3990
lock_init() at lock_init+0x43/frame 0xfffffe00934f39e0
_mtx_init() at _mtx_init+0x7c/frame 0xfffffe00934f3a20
g_nop_config() at g_nop_config+0x51a/frame 0xfffffe00934f3b30
g_ctl_req() at g_ctl_req+0x100/frame 0xfffffe00934f3b70
g_run_events() at g_run_events+0x1a7/frame 0xfffffe00934f3bb0
fork_exit() at fork_exit+0x84/frame 0xfffffe00934f3bf0
fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe00934f3bf0
--- trap 0, rip = 0, rsp = 0xfffffe00934f3cb0, rbp = 0 ---

(kgdb) bt 
#0  doadump (textdump=1) at pcpu.h:219
#1  0xffffffff808bbb57 in kern_reboot (howto=260) at /usr/src/sys/kern/kern_shutdown.c:447
#2  0xffffffff808bc065 in vpanic (fmt=<value optimized out>, ap=<value optimized out>) at /usr/src/sys/kern/kern_shutdown.c:754
#3  0xffffffff808bbef6 in kassert_panic (fmt=<value optimized out>) at /usr/src/sys/kern/kern_shutdown.c:642
#4  0xffffffff808f47c3 in lock_init (lock=0xfffff80002566640, class=0xffffffff813e9ce0, name=0xffffffff81c947ce "gnop lock", type=0x0, flags=131072) at /usr/src/sys/kern/subr_lock.c:81
#5  0xffffffff808a8acc in _mtx_init (c=0xfffff80002566658, name=0xffffffff81c947ce "gnop lock", type=0x0, opts=<value optimized out>) at /usr/src/sys/kern/kern_mutex.c:905
#6  0xffffffff81c9351a in g_nop_config (req=0xfffff800052a48c0, mp=0xffffffff81c94a20, verb=<value optimized out>) at /usr/src/sys/modules/geom/geom_nop/../../../geom/nop/g_nop.c:229
#7  0xffffffff8081d790 in g_ctl_req (arg=0xfffff800052a48c0, flag=<value optimized out>) at /usr/src/sys/geom/geom_ctl.c:454
#8  0xffffffff80820d27 in g_run_events () at /usr/src/sys/geom/geom_event.c:257
#9  0xffffffff8088b094 in fork_exit (callout=0xffffffff80822df0 <g_event_procbody>, arg=0x0, frame=0xfffffe00934f3c00) at /usr/src/sys/kern/kern_fork.c:995
#10 0xffffffff80c9bf4e in fork_trampoline () at /usr/src/sys/amd64/amd64/exception.S:606
#11 0x0000000000000000 in ?? ()
Current language:  auto; currently minimal
(kgdb)

...keith