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 14:49:40 +0200
From:	Michal Kubecek <mkubecek@...e.cz>
To:	Nicolas Dichtel <nicolas.dichtel@...nd.com>
Cc:	"David S. Miller" <davem@...emloft.net>, 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

On Wed, May 13, 2015 at 02:28:57PM +0200, Nicolas Dichtel wrote:
> 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?

It does not, sorry. I'm still trying to find out what did I wrong while
testing. I'll need to move the initialization of remaining above the
label.

                                                         Michal Kubecek

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