netdev - Re: [PATCH net-next] udp: expand SKB_DROP_REASON_UDP

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Message-ID: <CANn89i+QnSwxB33Hp48587EWAX=QYY0Msmv_bkfe_C1amk8Ftg@mail.gmail.com>
Date: Thu, 6 Mar 2025 20:12:26 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Willem de Bruijn <willemb@...gle.com>, David Ahern <dsahern@...nel.org>, 
	Simon Horman <horms@...nel.org>, netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net-next] udp: expand SKB_DROP_REASON_UDP_CSUM use

On Thu, Mar 6, 2025 at 8:01 PM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>
> Eric Dumazet wrote:
> > Use SKB_DROP_REASON_UDP_CSUM in __first_packet_length()
> > and udp_read_skb() when dropping a packet because of
> > a wrong UDP checksum.
> >
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> > ---
> >  net/ipv4/udp.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> > index 17c7736d8349433ad2d4cbcc9414b2f8112610af..39c3adf333b5f02ca53f768c918c75f2fc7f93ac 100644
> > --- a/net/ipv4/udp.c
> > +++ b/net/ipv4/udp.c
> > @@ -1848,7 +1848,7 @@ static struct sk_buff *__first_packet_length(struct sock *sk,
> >                       atomic_inc(&sk->sk_drops);
> >                       __skb_unlink(skb, rcvq);
> >                       *total += skb->truesize;
> > -                     kfree_skb(skb);
> > +                     kfree_skb_reason(skb, SKB_DROP_REASON_UDP_CSUM);
> >               } else {
> >                       udp_skb_csum_unnecessary_set(skb);
> >                       break;
> > @@ -2002,7 +2002,7 @@ int udp_read_skb(struct sock *sk, skb_read_actor_t recv_actor)
> >               __UDP_INC_STATS(net, UDP_MIB_CSUMERRORS, is_udplite);
> >               __UDP_INC_STATS(net, UDP_MIB_INERRORS, is_udplite);
> >               atomic_inc(&sk->sk_drops);
> > -             kfree_skb(skb);
> > +             kfree_skb_reason(skb, SKB_DROP_REASON_UDP_CSUM);
> >               goto try_again;
> >       }
>
> From a quick search for UDP_MIB_CSUMERRORS, one more case with regular
> kfree_skb:
>
> csum_copy_err:
>         if (!__sk_queue_drop_skb(sk, &udp_sk(sk)->reader_queue, skb, flags,
>                                  udp_skb_destructor)) {
>                 UDP_INC_STATS(sock_net(sk), UDP_MIB_CSUMERRORS, is_udplite);
>                 UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
>         }
>         kfree_skb(skb);

Right, I was unsure because of the conditional SNMP updates.