netdev - Re: [PATCHv5 net 0/8] disable neigh update for tunnels during pmtu update

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Date:   Tue, 24 Dec 2019 22:30:43 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     liuhangbin@...il.com
Cc:     netdev@...r.kernel.org, ja@....bg, marcelo.leitner@...il.com,
        dsahern@...il.com, edumazet@...gle.com, gnault@...hat.com,
        pablo@...filter.org, stephen@...workplumber.org,
        alexey.kodanev@...cle.com
Subject: Re: [PATCHv5 net 0/8] disable neigh update for tunnels during pmtu
 update

From: Hangbin Liu <liuhangbin@...il.com>
Date: Sun, 22 Dec 2019 10:51:08 +0800

> 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.
 ...

Series applied and queued up for -stable, thanks.