netdev - Re: [PATCH net-next 1/8] udp: fixup csum for GSO receive slow path

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Date:   Tue, 23 Mar 2021 21:49:10 -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 1/8] udp: fixup csum for GSO receive slow path

> > > > @@ -2168,6 +2168,7 @@ static int udp_queue_rcv_one_skb(struct sock *sk, struct sk_buff *skb)
> > > >  static int udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
> > > >  {
> > > >         struct sk_buff *next, *segs;
> > > > +       int csum_level;
> > > >         int ret;
> > > >
> > > >         if (likely(!udp_unexpected_gso(sk, skb)))
> > > > @@ -2175,9 +2176,18 @@ static int udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
> > > >
> > > >         BUILD_BUG_ON(sizeof(struct udp_skb_cb) > SKB_GSO_CB_OFFSET);
> > > >         __skb_push(skb, -skb_mac_offset(skb));
> > > > +       csum_level = !!(skb_shinfo(skb)->gso_type &
> > > > +                       (SKB_GSO_UDP_TUNNEL | SKB_GSO_UDP_TUNNEL_CSUM));
> > > >         segs = udp_rcv_segment(sk, skb, true);
> > > >         skb_list_walk_safe(segs, skb, next) {
> > > >                 __skb_pull(skb, skb_transport_offset(skb));
> > > > +
> > > > +               /* UDP GSO packets looped back after adding UDP encap land here with CHECKSUM none,
> > > > +                * instead of adding another check in the tunnel fastpath, we can force valid
> > > > +                * csums here (packets are locally generated).
> > > > +                * Additionally fixup the UDP CB
> > > > +                */

Btw, instead of this comment plus a comment in the ipv6 code that
points back to this ipv4 comment, I would move the explanation to
the udp_post_segment_fix_csum function itself.