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 06:30:20 -0700
From:	roopa <roopa@...ulusnetworks.com>
To:	Michal Kubecek <mkubecek@...e.cz>
CC:	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	"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 5/13/15, 5:49 AM, Michal Kubecek wrote:
> 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.
>
This looks like a similar bug i was trying to fix some time back:
http://patchwork.ozlabs.org/patch/362296/

(I am not sure if my full patch is still valid. I was thinking of 
re-spining it sometime soon. If you are interested in trying it out, 
please do)
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