linux-kernel - Re: [PATCH net v3 2/2] ipv6: fix ECMP route replacement

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Date:	Wed, 20 May 2015 10:56:31 +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>,
	roopa <roopa@...ulusnetworks.com>
Subject: Re: [PATCH net v3 2/2] ipv6: fix ECMP route replacement

Le 18/05/2015 20:54, Michal Kubecek a écrit :
> When replacing an IPv6 multipath route with "ip route replace", i.e.
> NLM_F_CREATE | NLM_F_REPLACE, fib6_add_rt2node() replaces only first
> matching route without fixing its siblings, resulting in corrupted
> siblings linked list; removing one of the siblings can then end in an
> infinite loop.
>
> IPv6 ECMP implementation is a bit different from IPv4 so that route
> replacement cannot work in exactly the same way. This should be a
> reasonable approximation:
>
> 1. If the new route is ECMP-able and there is a matching ECMP-able one
> already, replace it and all its siblings (if any).
>
> 2. If the new route is ECMP-able and no matching ECMP-able route exists,
> replace first matching non-ECMP-able (if any) or just add the new one.
>
> 3. If the new route is not ECMP-able, replace first matching
> non-ECMP-able route (if any) or add the new route.
>
> We also need to remove the NLM_F_REPLACE flag after replacing old
> route(s) by first nexthop of an ECMP route so that each subsequent
> nexthop does not replace previous one.
>
> Fixes: 51ebd3181572 ("ipv6: add support of equal cost multipath (ECMP)")
> Signed-off-by: Michal Kubecek <mkubecek@...e.cz>
LGTM.
Acked-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
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