kernel panic in wireless-related sysctl walk

With 'device iwn' and all the related wireless bits compiled into a
custom kernel for a laptop, executing 'sysctl -a' yields a kernel panic
of the form ..

Fatal trap 12: page fault while in kernel mode
cpuid = 1; apic id = 01
fault virtual address   = 0x8
fault code              = supervisor read data, page not present
instruction pointer     = 0x20:0xffffffff809bf22c
stack pointer           = 0x28:0xfffffe0097fb7660
frame pointer           = 0x28:0xfffffe0097fb7670
code segment            = base 0x0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, long 1, def32 0, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0
current process         = 11053 (sysctl)
trap number             = 12
panic: page fault
cpuid = 1
time = 1547129798
Uptime: 3d10h27m14s
Dumping 3840 out of 16258
MB:..1%..11%..21%..31%..41%..51%..61%..71%..81%..91%

 [ .. ]

(kgdb) #0  doadump (textdump=<value optimized out>) at pcpu.h:230
#1  0xffffffff808704eb in kern_reboot (howto=260)
    at /usr/src/sys/kern/kern_shutdown.c:451
#2  0xffffffff80870920 in vpanic (fmt=<value optimized out>,
    ap=<value optimized out>) at /usr/src/sys/kern/kern_shutdown.c:877
#3  0xffffffff80870753 in panic (fmt=<value optimized out>)
    at /usr/src/sys/kern/kern_shutdown.c:804
#4  0xffffffff80c63b5b in trap_fatal (frame=0xfffffe0097fb75a0, eva=8)
    at /usr/src/sys/amd64/amd64/trap.c:929
#5  0xffffffff80c63f10 in trap_pfault (frame=0xfffffe0097fb75a0, usermode=0)
    at /usr/src/sys/amd64/amd64/trap.c:839
#6  0xffffffff80c632be in trap (frame=0xfffffe0097fb75a0)
    at /usr/src/sys/amd64/amd64/trap.c:441
#7  0xffffffff80c40535 in calltrap ()
    at /usr/src/sys/amd64/amd64/exception.S:232
#8  0xffffffff809bf22c in amrr_node_stats (ni=0xfffffe008cf83000,
    s=0xfffffe0097fb76f0) at /usr/src/sys/net80211/ieee80211_amrr.c:464
#9  0xffffffff809ef9f4 in ieee80211_ratectl_sysctl_stats_node_iter (
    arg=0xfffffe0097fb76f0, ni=0xfffffe008cf83000) at
ieee80211_ratectl.h:170
#10 0xffffffff809e42b0 in ieee80211_iterate_nodes_vap (
    nt=<value optimized out>, vap=<value optimized out>,
    f=0xffffffff809ef9b0 <ieee80211_ratectl_sysctl_stats_node_iter>,
    arg=0xfffffe0097fb76f0) at /usr/src/sys/net80211/ieee80211_node.c:2558
#11 0xffffffff809ef941 in ieee80211_ratectl_sysctl_stats (
    oidp=<value optimized out>, arg1=<value optimized out>,
    arg2=<value optimized out>, req=<value optimized out>)
    at /usr/src/sys/net80211/ieee80211_ratectl.c:99
#12 0xffffffff8087f8ab in sysctl_root_handler_locked
(oid=0xfffff80016697d00,
    arg1=0xfffff80007bef000, arg2=0, req=0xfffffe0097fb7840,
    tracker=0xfffffe0097fb77b8) at /usr/src/sys/kern/kern_sysctl.c:166
#13 0xffffffff8087ef4f in sysctl_root (arg1=0xfffff80007bef000, arg2=0,
    req=0xfffffe0097fb7840) at /usr/src/sys/kern/kern_sysctl.c:2080
#14 0xffffffff8087f5ca in userland_sysctl (td=0xfffff80007d96000,
    name=0xfffffe0097fb7900, namelen=4, old=<value optimized out>,
    oldlenp=<value optimized out>, inkernel=<value optimized out>, new=0x0,
    newlen=0, retval=0xfffffe0097fb7968, flags=0)
    at /usr/src/sys/kern/kern_sysctl.c:2175
#15 0xffffffff8087f40f in sys___sysctl (td=0xfffff80007d96000,
    uap=0xfffff80007d963c0) at /usr/src/sys/kern/kern_sysctl.c:2110
#16 0xffffffff80c64742 in amd64_syscall (td=0xfffff80007d96000, traced=0)
    at subr_syscall.c:135
#17 0xffffffff80c40e1d in fast_syscall_common ()
    at /usr/src/sys/amd64/amd64/exception.S:504

What other data should I capture to assist in identifying and resolving
this?

	imb