regression (between Apr 16-23) panic in swi4 clock sio

Transcribed manually, expect typos. Fairly reproducible, please
request further info if necessary.

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<kernel boots>
...
rl0: link state changed to DOWN
rl0: flags ... status: no carrier
enc0: ...
...
net.inet6.ip6.forwarding: 0 -> 0
net.inet6.ip6.accept rtadv: 1 -> 1
checking if rl0 is ready...
rl0 is tentative
Fatal trap 12: page fault while in kernel mode
cpuid = 0; apic id = 00
fault virtual address = 0x0
fault code = supervisor read instruction, page not present
instruction pointer = 0x8:0x0
stack pointer = 0x10:0xffffffffab465690
frame pointer = 0x10:0xffffffffab465720
code segment = base 0x0, limit 0xffff, type 0x1b
             = DPL 0, pres 1, long 1, det32 0, gran 1
processor eflags = interrupt enabled, resume, IOPL = 0
current process = 12 (swi4: clos sio)
[thread pid 12 tid 100005]
Stopped at 0: *** error reading from address 0 ***
db> bt
Tracing pid 12 tid 100005 td 0xffffff00010ed000
uart_z8530_class() at 0
ip6_output() at ip6_output+0x1562
nd6_ns_output() at nd6_ns_output+0x3de
nd6_dad_timer() at nd6_dad_timer+0x29a
softclock() at softclock+0x2ff
ithread_loop() at ithread_loop+0x180
fork_exit() at fork_exit+0x1ff
fork_trampoline() at fork_trampoline+0xe
--- trap 0, rip = 0, rsp = 0xffffffffab465d30, rbp = 0 ---
db> ps
pid ppid pgrp uid state wmesg wchan cmd
545 528 28 0 S+ select 0xffffff0001712750 rtsol
527 28 28 0 S+ wait 0xffffff00012cc440 sh
...
10005 Run CPU 0 [swi4: clock sio]
...
10003 Run CPU 1 [idle: cpu1]
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include		GENERIC
ident		AMILO

nooption	SCHED_4BSD
option		SCHED_ULE

nooption	INVARIANTS
nooption	INVARIANT_SUPPORT
nooption	WITNESS
nooption	WITNESS_SKIPSPIN

nodevice	umass
device		atausb

option		IPSEC
option		IPSEC_FILTERTUNNEL
device		crypto
device		cryptodev
device		enc

option		IPFIREWALL
option		IPFIREWALL_FORWARD
option		IPFIREWALL_NAT
option		IPFIREWALL_DEFAULT_TO_ACCEPT
option		LIBALIAS

option		COMPAT_LINUX32
option		QUOTA
==========================================================
KERNCONF=	AMILO
CFLAGS+=	-DMALLOC_PRODUCTION
...
==========================================================
export LANG=en_US.UTF-8 MM_CHARSET=UTF-8
hostname="amilo.cenkes.org"
defaultrouter="192.168.18.33"
ifconfig_lo0_alias0="inet 127.0.0.2/32"
ifconfig_ath0="down"
ifconfig_rl0="inet 192.168.18.68/24"

sendmail_enable="NONE"
sshd_enable="YES"
linux_enable="YES"
moused_nondefault_enable="YES"
moused_enable="YES"
ftpd_enable="YES"
gateway_enable="YES"
background_fsck="NO"
fsck_y_enable="YES"
xfs_enable="YES"
ntpd_enable="YES"
kqemu_enable="YES"
nfs_server_enable="YES"
nfs_client_enable="YES"
rpcbind_enable="YES"
mountd_enable="YES"
nfsd_enable="YES"

ipv6_enable="YES"
ipv6_network_interfaces="rl0"
firewall_enable="YES"
firewall_type="/root/ipfw.rules"
rtsol_flags="-d"
powerd_enable="YES"
...
==========================================================