rtentry panic with FIB

Unfortunately it hung trying to dump, so all I have is the stack trace from 
DDB.  This is recent HEAD running stress2

panic: _mtx_lock_sleep: recursed on non-recursive mutex rtentry _at_ ../../1

cpuid = 1
KDB: enter: panic
[thread pid 14025 tid 100928 ]
Stopped at      kdb_enter+0x3d: movq    $0,0x435054(%rip)
db> tr
Tracing pid 14025 tid 100928 td 0xffffff0003773360
kdb_enter() at kdb_enter+0x3d
panic() at panic+0x14b
_mtx_lock_flags() at _mtx_lock_flags
_mtx_lock_flags() at _mtx_lock_flags+0xc3
rt_check_fib() at rt_check_fib+0x1ea
arpresolve() at arpresolve+0x77
ether_output() at ether_output+0x180
ip_output() at ip_output+0xb4f
udp_send() at udp_send+0x47d
sosend_dgram() at sosend_dgram+0x1fa
soo_write() at soo_write+0x30
dofilewrite() at dofilewrite+0x7a
kern_writev() at kern_writev+0x52
write() at write+0x4d
syscall() at syscall+0x1bf
Xfast_syscall() at Xfast_syscall+0xab
--- syscall (4, FreeBSD ELF64, write), rip = 0x80071cb7c, rsp = 
0x7fffffffe628,-
db> c
Uptime: 1h39m18s
Physical memory: 2038 MB
Dumping 263 MB:pid 14025 (udp), uid 26840, was killed: exceeded maximum CPU 
limt
pid 14099 (udp), uid 26840, was killed: exceeded maximum CPU limit
pid 14100 (udp), uid 26840, was killed: exceeded maximum CPU limit

-- 
John Baldwin