Re: [PATCH RFC 1/3] ipv6: Fix after pmtu events dissapearing host routes

[Martin Lau <kafai@fb.com>]

On Mon, Mar 30, 2015 at 12:33:13PM +0200, Steffen Klassert wrote:
> We currently don't clone host routes before we use them.
> If a pmtu event is received on such a route, it gets
> an expires value. As soon as the expiration time is
> elapsed, the route is deleted. As a result, the host
> es not reachable any more.
s/es/is

> We fix this by cloning host routes if they are not local,
> i.e. if pmtu events can happen. Also adjust the route
> deletion because the cached and the original host route
> are on the same fib node.
> 
> Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
> ---
>  net/ipv6/route.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index 4688bd4..4318626 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -961,7 +961,7 @@ redo_rt6_select:
>  
>  	if (!(rt->rt6i_flags & (RTF_NONEXTHOP | RTF_GATEWAY)))
>  		nrt = rt6_alloc_cow(rt, &fl6->daddr, &fl6->saddr);
> -	else if (!(rt->dst.flags & DST_HOST))
> +	else if (!(rt->dst.flags & DST_HOST) || !(rt->rt6i_flags & RTF_LOCAL))
>  		nrt = rt6_alloc_clone(rt, &fl6->daddr);
I suspect the nrt and rt will share the same inetpeer.  Hence, after the nrt is
removed, the MTU (obtained from PMTU update) will stay.

> @@ -1796,6 +1796,8 @@ static int ip6_route_del(struct fib6_config *cfg)
>  				continue;
>  			if (cfg->fc_metric && cfg->fc_metric != rt->rt6i_metric)
>  				continue;
> +			if (!(cfg->fc_flags & RTF_CACHE) && (rt->rt6i_flags & RTF_CACHE))
> +				continue;
>  			dst_hold(&rt->dst);
>  			read_unlock_bh(&table->tb6_lock);
>  
> @@ -2433,6 +2435,9 @@ static int rtm_to_fib6_config(struct sk_buff *skb, struct nlmsghdr *nlh,
>  	if (rtm->rtm_type == RTN_LOCAL)
>  		cfg->fc_flags |= RTF_LOCAL;
>  
> +	if (rtm->rtm_flags & RTM_F_CLONED)
> +		cfg->fc_flags |= RTF_CACHE;
> +
>  	cfg->fc_nlinfo.portid = NETLINK_CB(skb).portid;
>  	cfg->fc_nlinfo.nlh = nlh;
>  	cfg->fc_nlinfo.nl_net = sock_net(skb->sk);
I had pulled your last patch to my local branch that I am cooking.  I also
added similar changes to ip6_route_del() and rtm_to_fib_config(), and confirmed
it can keep 'ip -6 r del' and 'ip -6 r flush table cache' to keep working
properly.

Thanks,
--Martin