kern/50702: panic: bogus refcnt 0 (ARP)

[kardel%netbsd.org@localhost]

>Number:         50702
>Category:       kern
>Synopsis:       panic: kernel diagnostic assertion "(lle)->lle_refcnt > 0" failed: file "/fs/raid1a/src/NetBSD/cur/src/sys/net/if_llatbl.c", line 305 bogus refcnt 0 on lle 0xbad82a90
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Jan 24 17:10:00 +0000 2016
>Originator:     kardel%netbsd.org@localhost
>Release:        NetBSD 7.99.25 (20151229)
>Organization:
>Environment:
System: NetBSD xxxx 7.99.25 NetBSD 7.99.25 (RPI2SENSOR) #6: Tue Dec 29 11:37:46 CET 2015 kardel@xxxx:/fs/raid1a/src/NetBSD/cur/src/obj.evbarm/sys/arch/evbarm/compile/RPI2SENSOR evbarm
Architecture: earmv7hf
Machine: evbarm
>Description:
I did see the crash below on a RPI 2 (4 CPU). Additionally I observed that ARP resolution for the local network fails after a while, ping returned 'permission denied' if I remember right, definitely not a network related arror code.
. 
Dec 29 17:44:57 rpi /netbsd: arpresolve: valid llentry has no rtentry for 192.168.2.103 on usmsc0
Dec 29 17:44:57 rpi /netbsd: panic: kernel diagnostic assertion "(lle)->lle_refcnt > 0" failed: file "/fs/raid1a/src/NetBSD/cur/src/sys/net/if_llatbl.c", line 305 bogus refcnt 0 on lle 0xbad82a90
Dec 29 17:44:57 rpi /netbsd: cpu3: Begin traceback...
Dec 29 17:44:57 rpi /netbsd: 0xbac6594c: netbsd:db_panic+0xc
Dec 29 17:44:57 rpi /netbsd: 0xbac6597c: netbsd:vpanic+0x1b0
Dec 29 17:44:57 rpi /netbsd: 0xbac65994: netbsd:__udivmoddi4
Dec 29 17:44:57 rpi /netbsd: 0xbac659d4: netbsd:llentry_free+0x13c
Dec 29 17:44:57 rpi /netbsd: 0xbac65a14: netbsd:arp_rtrequest+0x550
Dec 29 17:44:57 rpi /netbsd: 0xbac65ae4: netbsd:rtrequest1+0x26c
Dec 29 17:44:57 rpi /netbsd: 0xbac65b2c: netbsd:rtrequest+0x58
Dec 29 17:44:57 rpi /netbsd: 0xbac65b84: netbsd:arpresolve+0x41c
Dec 29 17:44:57 rpi /netbsd: 0xbac65bc4: netbsd:ether_output+0x448
Dec 29 17:44:57 rpi /netbsd: 0xbac65bfc: netbsd:ip_hresolv_output+0x80
Dec 29 17:44:57 rpi /netbsd: 0xbac65ca4: netbsd:ip_output+0xe58
Dec 29 17:44:57 rpi /netbsd: 0xbac65cec: netbsd:rip_output+0x110
Dec 29 17:44:57 rpi /netbsd: 0xbac65d2c: netbsd:rip_send_wrapper+0x11c
Dec 29 17:44:57 rpi /netbsd: 0xbac65dbc: netbsd:sosend+0x734
Dec 29 17:44:57 rpi /netbsd: 0xbac65e74: netbsd:do_sys_sendmsg_so.isra.3+0x240
Dec 29 17:44:57 rpi /netbsd: 0xbac65eb4: netbsd:do_sys_sendmsg+0x90
Dec 29 17:44:57 rpi /netbsd: 0xbac65f04: netbsd:sys_sendto+0x60
Dec 29 17:44:57 rpi /netbsd: 0xbac65f7c: netbsd:syscall+0x84
Dec 29 17:44:57 rpi /netbsd: 0xbac65fac: netbsd:swi_handler+0xa0
Dec 29 17:44:57 rpi /netbsd: cpu3: End traceback...

Currently the crash pattern is observes twice a day.

>How-To-Repeat:
	difficult - when arp resolution stops it does not recover.
	panic occurs regularly, depending on network environment (maybe related to dhcpcd activity as
	I have not seen it in a static address assignment environment)
>Fix: