netdev - Re: [PATCH net 2/2] geneve, vxlan: Don't set exceptions if skb->len

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Message-ID: <CADvbK_fVyZA-MzmESYOQmp_pes+X61iftnYtNNU4Y_uqSg2LhQ@mail.gmail.com>
Date:   Mon, 15 Oct 2018 15:01:31 +0900
From:   Xin Long <lucien.xin@...il.com>
To:     Stefano Brivio <sbrivio@...hat.com>
Cc:     davem <davem@...emloft.net>, Sabrina Dubroca <sd@...asysnail.net>,
        network dev <netdev@...r.kernel.org>
Subject: Re: [PATCH net 2/2] geneve, vxlan: Don't set exceptions if skb->len < mtu

On Sat, Oct 13, 2018 at 6:54 AM Stefano Brivio <sbrivio@...hat.com> wrote:
>
> We shouldn't abuse exceptions: if the destination MTU is already higher
> than what we're transmitting, no exception should be created.
makes sense, shouldn't ip(6) tunnels also do this?

>
> Fixes: 52a589d51f10 ("geneve: update skb dst pmtu on tx path")
> Fixes: a93bf0ff4490 ("vxlan: update skb dst pmtu on tx path")
> Signed-off-by: Stefano Brivio <sbrivio@...hat.com>
> Reviewed-by: Sabrina Dubroca <sd@...asysnail.net>
> ---
>  drivers/net/geneve.c |  7 +++----
>  drivers/net/vxlan.c  |  4 ++--
>  include/net/dst.h    | 10 ++++++++++
>  3 files changed, 15 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/net/geneve.c b/drivers/net/geneve.c
> index 61c4bfbeb41c..493cd382b8aa 100644
> --- a/drivers/net/geneve.c
> +++ b/drivers/net/geneve.c
> @@ -830,8 +830,8 @@ static int geneve_xmit_skb(struct sk_buff *skb, struct net_device *dev,
>         if (IS_ERR(rt))
>                 return PTR_ERR(rt);
>
> -       skb_dst_update_pmtu(skb, dst_mtu(&rt->dst) -
> -                                GENEVE_IPV4_HLEN - info->options_len);
> +       skb_tunnel_check_pmtu(skb, &rt->dst,
> +                             GENEVE_IPV4_HLEN + info->options_len);
>
>         sport = udp_flow_src_port(geneve->net, skb, 1, USHRT_MAX, true);
>         if (geneve->collect_md) {
> @@ -872,8 +872,7 @@ static int geneve6_xmit_skb(struct sk_buff *skb, struct net_device *dev,
>         if (IS_ERR(dst))
>                 return PTR_ERR(dst);
>
> -       skb_dst_update_pmtu(skb, dst_mtu(dst) -
> -                                GENEVE_IPV6_HLEN - info->options_len);
> +       skb_tunnel_check_pmtu(skb, dst, GENEVE_IPV6_HLEN + info->options_len);
>
>         sport = udp_flow_src_port(geneve->net, skb, 1, USHRT_MAX, true);
>         if (geneve->collect_md) {
> diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
> index 22e0ce592e07..27bd586b94b0 100644
> --- a/drivers/net/vxlan.c
> +++ b/drivers/net/vxlan.c
> @@ -2194,7 +2194,7 @@ static void vxlan_xmit_one(struct sk_buff *skb, struct net_device *dev,
>                 }
>
>                 ndst = &rt->dst;
> -               skb_dst_update_pmtu(skb, dst_mtu(ndst) - VXLAN_HEADROOM);
> +               skb_tunnel_check_pmtu(skb, ndst, VXLAN_HEADROOM);
>
>                 tos = ip_tunnel_ecn_encap(tos, old_iph, skb);
>                 ttl = ttl ? : ip4_dst_hoplimit(&rt->dst);
> @@ -2231,7 +2231,7 @@ static void vxlan_xmit_one(struct sk_buff *skb, struct net_device *dev,
>                                 goto out_unlock;
>                 }
>
> -               skb_dst_update_pmtu(skb, dst_mtu(ndst) - VXLAN6_HEADROOM);
> +               skb_tunnel_check_pmtu(skb, ndst, VXLAN6_HEADROOM);
>
>                 tos = ip_tunnel_ecn_encap(tos, old_iph, skb);
>                 ttl = ttl ? : ip6_dst_hoplimit(ndst);
> diff --git a/include/net/dst.h b/include/net/dst.h
> index 7f735e76ca73..6cf0870414c7 100644
> --- a/include/net/dst.h
> +++ b/include/net/dst.h
> @@ -527,4 +527,14 @@ static inline void skb_dst_update_pmtu(struct sk_buff *skb, u32 mtu)
>                 dst->ops->update_pmtu(dst, NULL, skb, mtu);
>  }
>
> +static inline void skb_tunnel_check_pmtu(struct sk_buff *skb,
> +                                        struct dst_entry *encap_dst,
> +                                        int headroom)
> +{
> +       u32 encap_mtu = dst_mtu(encap_dst);
> +
> +       if (skb->len > encap_mtu - headroom)
> +               skb_dst_update_pmtu(skb, encap_mtu - headroom);
> +}
> +
>  #endif /* _NET_DST_H */
> --
> 2.19.1
>