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Date:   Mon, 13 Mar 2017 23:21:44 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     Sabrina Dubroca <sd@...asysnail.net>
Cc:     network dev <netdev@...r.kernel.org>,
        Michal Kubecek <mkubecek@...e.cz>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: Re: [PATCH net] ipv6: make ECMP route replacement less greedy

On Mon, Mar 13, 2017 at 8:28 PM, Sabrina Dubroca <sd@...asysnail.net> wrote:
> Commit 27596472473a ("ipv6: fix ECMP route replacement") introduced a
> loop that removes all siblings of an ECMP route that is being
> replaced. However, this loop doesn't stop when it has replaced
> siblings, and keeps removing other routes with a higher metric.
> We also end up triggering the WARN_ON after the loop, because after
> this nsiblings < 0.
>
> Instead, stop the loop when we have taken care of all routes with the
> same metric as the route being replaced.
>
>   Reproducer:
>   ===========
>     #!/bin/sh
>
>     ip netns add ns1
>     ip netns add ns2
>     ip -net ns1 link set lo up
>
>     for x in 0 1 2 ; do
>         ip link add veth$x netns ns2 type veth peer name eth$x netns ns1
>         ip -net ns1 link set eth$x up
>         ip -net ns2 link set veth$x up
>     done
>
>     ip -net ns1 -6 r a 2000::/64 nexthop via fe80::0 dev eth0 \
>             nexthop via fe80::1 dev eth1 nexthop via fe80::2 dev eth2
>     ip -net ns1 -6 r a 2000::/64 via fe80::42 dev eth0 metric 256
>     ip -net ns1 -6 r a 2000::/64 via fe80::43 dev eth0 metric 2048
>
>     echo "before replace, 3 routes"
>     ip -net ns1 -6 r | grep -v '^fe80\|^ff00'
>     echo
>
>     ip -net ns1 -6 r c 2000::/64 nexthop via fe80::4 dev eth0 \
>             nexthop via fe80::5 dev eth1 nexthop via fe80::6 dev eth2
>
>     echo "after replace, only 2 routes, metric 2048 is gone"
>     ip -net ns1 -6 r | grep -v '^fe80\|^ff00'
>
> Fixes: 27596472473a ("ipv6: fix ECMP route replacement")
> Signed-off-by: Sabrina Dubroca <sd@...asysnail.net>
Reviewed-by: Xin Long <lucien.xin@...il.com>

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