netdev - Re: [PATCH RFC] ipv6: fix route selection if kernel is not compiled with CONFIG_IPV6_ROUTER

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Date:	Wed, 10 Jul 2013 15:17:41 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Nicolas Dichtel <nicolas.dichtel@...nd.com>
Cc:	netdev@...r.kernel.org, yoshfuji@...ux-ipv6.org,
	petrus.lt@...il.com, davem@...emloft.net
Subject: Re: [PATCH RFC] ipv6: fix route selection if kernel is not compiled with CONFIG_IPV6_ROUTER_PREF

On Wed, Jul 10, 2013 at 02:08:42PM +0200, Nicolas Dichtel wrote:
> Le 10/07/2013 13:15, Hannes Frederic Sowa a écrit :
> >On Wed, Jul 10, 2013 at 09:54:58AM +0200, Nicolas Dichtel wrote:
> >>Le 09/07/2013 23:57, Hannes Frederic Sowa a écrit :
> >>>Are we sure we decrement all sibling's rt6i_nsiblings? Shouldn't we
> >>>start iterating from fn->leaf? But this does not seem to cause it,
> >>>because my trace does not report any calls to fib6_del_route.
> >>Note sure to follow you, but all siblings are listed in rt6i_siblings, so
> >>it must be enough.
> >
> >My hunch was to iterate over fn->leaf->rt_next and compare the metrics 
> >like we
> >do when adding a new route. Then take that rt6_info->rt6i_siblings 
> >list_head
> >to iterate over the remaining siblings. But I did not review that part
> >carefully, need to check later.
> >
> >>>You could try reproduce it by having an interface autoconfigured with
> >>>a default router with NUD_VALID neighbour. I then added an unused vlan
> >>>interface (vid 100 in my case) and added the following ip addresses:
> >>>
> >>>ip -6 a a 2001:ffff::1/64 dev eth0.100
> >>>ip -6 r a 2000::/3 nexthop via 2001:ffff::30 nexthop via 2001:ffff::31
> >>>nexthop via 2001:ffff::32 nexthop via 2001:ffff::33
> >>>
> >>>(all nexthops should not be reachable)
> >>>
> >>>After starting a ping6 2000::1 the box should panic soon, after the
> >>>first nexthop entry times out.
> >>>
> >>>Perhaps you could give me a hint?
> >>I will run some tests with your patch. Will see.
> >>
> >>I assume you didn't reproduce this without your patch.
> >
> >Current kernel does not correctly select more specific routes, so these 
> >routes
> >are not even tried and the logic should not be excercised.
> >
> >Ah, sorry, you should also compile your kernel without
> >CONFIG_IPV6_ROUTER_PREF, too, if you try to reproduce it.
> I've done this.
> 
> My conf (eth1 autoconfigured, I use net-next + your patch):
> vconfig add eth1 100
> ifconfig eth1.100 up
> ip -6 a a 2001:ffff::1/64 dev eth1.100
> ip -6 r a 2000::/3 nexthop via 2001:ffff::30 nexthop via 2001:ffff::31 
> nexthop via 2001:ffff::32 nexthop via 2001:ffff::33
> ping6 2000::1

Hm, I see. I suspect something with timing. I, too, use a net-next and have
one function dump_route added and sprinkeld it at some points.

When I copy&pasted your calls I could not reproduce it. After a reboot when
just applying the commands from my history (which I did a lot faster), I got
the panic again.

I'll remove the dump_routes and recheck later.

Thanks,

  Hannes


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