(kgdb) where
#0  __curthread () at /usr/src/sys/amd64/include/pcpu.h:234
#1  doadump (textdump=<optimized out>) at /usr/src/sys/kern/kern_shutdown.c:371
#2  0xffffffff80bd0228 in kern_reboot (howto=260) at /usr/src/sys/kern/kern_shutdown.c:451
#3  0xffffffff80bd0689 in vpanic (fmt=<optimized out>, ap=<optimized out>)
    at /usr/src/sys/kern/kern_shutdown.c:877
#4  0xffffffff80bd0483 in panic (fmt=<unavailable>) at /usr/src/sys/kern/kern_shutdown.c:804
#5  0xffffffff810a7dcc in trap_fatal (frame=0xfffffe0000734700, eva=1040)
    at /usr/src/sys/amd64/amd64/trap.c:943
#6  0xffffffff810a7e19 in trap_pfault (frame=0xfffffe0000734700, usermode=0)
    at /usr/src/sys/amd64/amd64/trap.c:767
#7  0xffffffff810a740f in trap (frame=0xfffffe0000734700)
    at /usr/src/sys/amd64/amd64/trap.c:443
#8  <signal handler called>
#9  __mtx_lock_sleep (c=0xfffff8340b76a1a0, v=<optimized out>)
    at /usr/src/sys/kern/kern_mutex.c:565
#10 0xffffffff80ccd641 in if_delgroups (ifp=<optimized out>) at /usr/src/sys/net/if.c:1558
#11 if_detach_internal (ifp=0xfffff8340b76a000, vmove=1, ifcp=0xfffffe00007348d8)
    at /usr/src/sys/net/if.c:1117
#12 0xffffffff80cd496c in if_vmove (ifp=0xfffff8340b76a000, new_vnet=0xfffff8205001aa80)
    at /usr/src/sys/net/if.c:1263
#13 0xffffffff80cd4918 in vnet_if_return (unused=<optimized out>)
    at /usr/src/sys/net/if.c:487
#14 0xffffffff80cfe324 in vnet_sysuninit () at /usr/src/sys/net/vnet.c:597
#15 vnet_destroy (vnet=0xfffff833cf77dec0) at /usr/src/sys/net/vnet.c:284
#16 0xffffffff80b988d0 in prison_deref (pr=0xffffffff81b0c7f0 <prison0>, flags=20)
    at /usr/src/sys/kern/kern_jail.c:2640
#17 0xffffffff80c2fad4 in taskqueue_run_locked (queue=0xfffff80103c2c800)
    at /usr/src/sys/kern/subr_taskqueue.c:467
#18 0xffffffff80c30e08 in taskqueue_thread_loop (arg=<optimized out>)
    at /usr/src/sys/kern/subr_taskqueue.c:773
#19 0xffffffff80b90c43 in fork_exit (callout=0xffffffff80c30d70 <taskqueue_thread_loop>, 
    arg=0xffffffff8200ccf0 <taskqueue_thread>, frame=0xfffffe0000734a80)
    at /usr/src/sys/kern/kern_fork.c:1065
#20 <signal handler called>