Subject: Re: [PATCH net-next 0/8] disable neigh update for tunnels during pmtu update

From: Guillaume Nault <[email-masked]>
Date: Thu, 19 Dec 2019 18:53:53 +0100

On Wed, Dec 18, 2019 at 07:53:05PM +0800, Hangbin Liu wrote:
> When we setup a pair of gretap, ping each other and create neighbour cache.
> Then delete and recreate one side. We will never be able to ping6 to the new
> created gretap.
> 
> The reason is when we ping6 remote via gretap, we will call like
> 
> gre_tap_xmit()
>  - ip_tunnel_xmit()
>    - tnl_update_pmtu()
>      - skb_dst_update_pmtu()
>        - ip6_rt_update_pmtu()
>          - __ip6_rt_update_pmtu()
>            - dst_confirm_neigh()
>              - ip6_confirm_neigh()
>                - __ipv6_confirm_neigh()
>                  - n->confirmed = now
> 
> As the confirmed time updated, in neigh_timer_handler() the check for
> NUD_DELAY confirm time will pass and the neigh state will back to
> NUD_REACHABLE. So the old/wrong mac address will be used again.
> 
> If we do not update the confirmed time, the neigh state will go to
> neigh->nud_state = NUD_PROBE; then go to NUD_FAILED and re-create the
> neigh later, which is what IPv4 does.
> 
> We couldn't remove the ip6_confirm_neigh() directly as we still need it
> for TCP flows. To fix it, we have to pass a bool parameter to
> dst_ops.update_pmtu() and only disable neighbor update for tunnels.
> 

Apart from the missing Fixes tags, code looks good to me.

Reviewed-by: Guillaume Nault <[email-masked]>