Bug 251600

I try to use a Raspi4 as DSL router. That works fine with mpd5. For IPv6 I use dhcpcd but when I try my setup with CURRENT the kernel panics (with Raspi3 or Raspi4) when I start dhcpcd. With a Raspi3 and 12.1 the same setup works fine.

Here the panic:

panic: prefix 0xffffa000060c6000 has referencing addresses
cpuid = 0
time = 1607078839
KDB: stack backtrace:
db_trace_self() at db_trace_self_wrapper+0x30
	 pc = 0xffff00000055ae28  lr = 0xffff00000005eb10
	 sp = 0xffff00061d8dae40  fp = 0xffff00061d8db050

db_trace_self_wrapper() at vpanic+0x194
	 pc = 0xffff00000005eb10  lr = 0xffff00000029346c
	 sp = 0xffff00061d8db060  fp = 0xffff00061d8db0e0

vpanic() at panic+0x44
	 pc = 0xffff00000029346c  lr = 0xffff0000002934f8
	 sp = 0xffff00061d8db0f0  fp = 0xffff00061d8db170

panic() at nd6_prefix_del+0x224
	 pc = 0xffff0000002934f8  lr = 0xffff00000052f1dc
	 sp = 0xffff00061d8db180  fp = 0xffff00061d8db2d0

nd6_prefix_del() at nd6_ioctl+0x54c
	 pc = 0xffff00000052f1dc  lr = 0xffff00000052d6dc
	 sp = 0xffff00061d8db2e0  fp = 0xffff00061d8db310

nd6_ioctl() at ifioctl+0x528
	 pc = 0xffff00000052d6dc  lr = 0xffff0000005729dc
	 sp = 0xffff00061d8db320  fp = 0xffff00061d8db3d0

ifioctl() at kern_ioctl+0x2ec
	 pc = 0xffff0000005729dc  lr = 0xffff00000055c874
	 sp = 0xffff00061d8db3e0  fp = 0xffff00061d8db4f0

kern_ioctl() at sys_ioctl+0x144
	 pc = 0xffff00000055c874  lr = 0xffff00005996674c
	 sp = 0xffff00061d8db500  fp = 0xffff00061d8db580

sys_ioctl() at do_el0_sync+0x454
	 pc = 0xffff00005996674c  lr = 0xffff00000039e000
	 sp = 0xffff00061d8db590  fp = 0xffff00061d8db5b0

do_el0_sync() at handle_el0_sync+0x90
	 pc = 0xffff00000039e000  lr = 0xffff000000266a68
	 sp = 0xffff00061d8db5c0  fp = 0xffff00061d8db8e0

handle_el0_sync() at 0x251e84
	 pc = 0xffff000000266a68  lr = 0xffff000000268120
	 sp = 0xffff00061d8db8f0  fp = 0xffff00061d8db920

KDB: enter: panic
[ thread pid 1260 tid 100123 ]
Stopped at     0x40459e44

(the values of the registers are not correct since I only had a
screenshot of the panic and needed to type it in by hand and used
another panic as template, the rest is correct though)