netdev - Re: [PATCH net-next 3/8] udp: properly complete L4 GRO over UDP tunnel packet

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Date:   Mon, 22 Mar 2021 09:30:55 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Alexander Lobakin <alobakin@...me>
Subject: Re: [PATCH net-next 3/8] udp: properly complete L4 GRO over UDP
 tunnel packet

On Sun, Mar 21, 2021 at 1:01 PM Paolo Abeni <pabeni@...hat.com> wrote:
>
> After the previous patch the stack can do L4 UDP aggregation
> on top of an UDP tunnel.
>
> The current GRO complete code tries frag based aggregation first;
> in the above scenario will generate corrupted frames.
>
> We need to try first UDP tunnel based aggregation, if the GRO
> packet requires that. We can use time GRO 'encap_mark' field
> to track the need GRO complete action. If encap_mark is set,
> skip the frag_list aggregation.
>
> On tunnel encap GRO complete clear such field, so that an inner
> frag_list GRO complete could take action.
>
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> ---
>  net/ipv4/udp_offload.c | 8 +++++++-
>  net/ipv6/udp_offload.c | 3 ++-
>  2 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
> index 25134a3548e99..54e06b88af69a 100644
> --- a/net/ipv4/udp_offload.c
> +++ b/net/ipv4/udp_offload.c
> @@ -642,6 +642,11 @@ int udp_gro_complete(struct sk_buff *skb, int nhoff,
>                 skb_shinfo(skb)->gso_type = uh->check ? SKB_GSO_UDP_TUNNEL_CSUM
>                                         : SKB_GSO_UDP_TUNNEL;
>
> +               /* clear the encap mark, so that inner frag_list gro_complete
> +                * can take place
> +                */
> +               NAPI_GRO_CB(skb)->encap_mark = 0;
> +
>                 /* Set encapsulation before calling into inner gro_complete()
>                  * functions to make them set up the inner offsets.
>                  */
> @@ -665,7 +670,8 @@ INDIRECT_CALLABLE_SCOPE int udp4_gro_complete(struct sk_buff *skb, int nhoff)
>         const struct iphdr *iph = ip_hdr(skb);
>         struct udphdr *uh = (struct udphdr *)(skb->data + nhoff);
>
> -       if (NAPI_GRO_CB(skb)->is_flist) {
> +       /* do fraglist only if there is no outer UDP encap (or we already processed it) */
> +       if (NAPI_GRO_CB(skb)->is_flist && !NAPI_GRO_CB(skb)->encap_mark) {

Sorry, I don't follow. I thought the point was to avoid fraglist if an
outer udp tunnel header is present. But the above code clears the mark
and allows entering the fraglist branch exactly when such a header is
encountered?

>                 uh->len = htons(skb->len - nhoff);
>
>                 skb_shinfo(skb)->gso_type |= (SKB_GSO_FRAGLIST|SKB_GSO_UDP_L4);
> diff --git a/net/ipv6/udp_offload.c b/net/ipv6/udp_offload.c
> index faa823c242923..b3d9ed96e5ea5 100644
> --- a/net/ipv6/udp_offload.c
> +++ b/net/ipv6/udp_offload.c
> @@ -163,7 +163,8 @@ INDIRECT_CALLABLE_SCOPE int udp6_gro_complete(struct sk_buff *skb, int nhoff)
>         const struct ipv6hdr *ipv6h = ipv6_hdr(skb);
>         struct udphdr *uh = (struct udphdr *)(skb->data + nhoff);
>
> -       if (NAPI_GRO_CB(skb)->is_flist) {
> +       /* do fraglist only if there is no outer UDP encap (or we already processed it) */
> +       if (NAPI_GRO_CB(skb)->is_flist && !NAPI_GRO_CB(skb)->encap_mark) {
>                 uh->len = htons(skb->len - nhoff);
>
>                 skb_shinfo(skb)->gso_type |= (SKB_GSO_FRAGLIST|SKB_GSO_UDP_L4);
> --
> 2.26.2
>