netdev - Re: [PATCH net 1/2] ipv6: do not delete previously existing ECMP routes if add fails

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Date:	Wed, 13 May 2015 14:28:57 +0200
From:	Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:	Michal Kubecek <mkubecek@...e.cz>,
	"David S. Miller" <davem@...emloft.net>
CC:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH net 1/2] ipv6: do not delete previously existing ECMP
 routes if add fails

Le 13/05/2015 11:50, Michal Kubecek a écrit :
> If adding a nexthop of an IPv6 multipath route fails, comment in
> ip6_route_multipath() says we are going to delete all nexthops already
> added. However, current implementation deletes even the routes it
> hasn't even tried to add yet. For example, running
>
>    ip route add 1234:5678::/64 \
>        nexthop via fe80::aa dev dummy1 \
>        nexthop via fe80::bb dev dummy1 \
>        nexthop via fe80::cc dev dummy1
>
> twice results in removing all routes first command added.
>
> Limit the second (delete) run to nexthops that succeeded in the first
> (add) run.
>
> Fixes: 51ebd3181572 ("ipv6: add support of equal cost multipath (ECMP)")
> Signed-off-by: Michal Kubecek <mkubecek@...e.cz>
> ---
>   net/ipv6/route.c | 1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index d3588885f097..18b92c05b541 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -2536,6 +2536,7 @@ beginning:
>   				 * next hops that have been already added.
>   				 */
>   				add = 0;
> +				remaining = cfg->fc_mp_len - remaining;
>   				goto beginning;
Not sure to understand your fix. At the label beginning, the code is:

beginning:
         rtnh = (struct rtnexthop *)cfg->fc_mp;
         remaining = cfg->fc_mp_len;

Hence, 'remaining' will be overridden. How does your patch work?
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