linux-kernel - RE: [PATCH net-next] udp: allow forwarding of plain (non-fraglisted) UDP GRO packets

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Date:   Wed, 13 Jan 2021 12:59:45 +0900
From:   "Dongseok Yi" <dseok.yi@...sung.com>
To:     "'Alexander Duyck'" <alexander.duyck@...il.com>,
        "'Alexander Lobakin'" <alobakin@...me>,
        "'David S. Miller'" <davem@...emloft.net>,
        "'Jakub Kicinski'" <kuba@...nel.org>
Cc:     "'Eric Dumazet'" <edumazet@...gle.com>,
        "'Edward Cree'" <ecree@...arflare.com>,
        "'Willem de Bruijn'" <willemb@...gle.com>,
        "'Steffen Klassert'" <steffen.klassert@...unet.com>,
        "'Alexey Kuznetsov'" <kuznet@....inr.ac.ru>,
        "'Hideaki YOSHIFUJI'" <yoshfuji@...ux-ipv6.org>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH net-next] udp: allow forwarding of plain
 (non-fraglisted) UDP GRO packets

On 2021-01-13 12:10, Alexander Duyck wrote:
> On 1/12/21 1:16 PM, Alexander Lobakin wrote:
> > Commit 9fd1ff5d2ac7 ("udp: Support UDP fraglist GRO/GSO.") actually
> > not only added a support for fraglisted UDP GRO, but also tweaked
> > some logics the way that non-fraglisted UDP GRO started to work for
> > forwarding too.
> > Tests showed that currently forwarding and NATing of plain UDP GRO
> > packets are performed fully correctly, regardless if the target
> > netdevice has a support for hardware/driver GSO UDP L4 or not.
> > Add the last element and allow to form plain UDP GRO packets if
> > there is no socket -> we are on forwarding path.
> >

Your patch is very similar with the RFC what I submitted but has
different approach. My concern was NAT forwarding.
https://lore.kernel.org/patchwork/patch/1362257/

Nevertheless, I agreed with your idea that allow fraglisted UDP GRO
if there is socket.

> > Plain UDP GRO forwarding even shows better performance than fraglisted
> > UDP GRO in some cases due to not wasting one skbuff_head per every
> > segment.
> >
> > Signed-off-by: Alexander Lobakin <alobakin@...me>
> > ---
> >   net/ipv4/udp_offload.c | 5 +++--
> >   1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
> > index ff39e94781bf..9d71df3d52ce 100644
> > --- a/net/ipv4/udp_offload.c
> > +++ b/net/ipv4/udp_offload.c
> > @@ -460,12 +460,13 @@ struct sk_buff *udp_gro_receive(struct list_head *head, struct sk_buff *skb,
> >   	if (skb->dev->features & NETIF_F_GRO_FRAGLIST)
> >   		NAPI_GRO_CB(skb)->is_flist = sk ? !udp_sk(sk)->gro_enabled: 1;

is_flist can be true even if !sk.

> >
> > -	if ((sk && udp_sk(sk)->gro_enabled) || NAPI_GRO_CB(skb)->is_flist) {
> > +	if (!sk || (sk && udp_sk(sk)->gro_enabled) ||

Actually sk would be NULL by udp_encap_needed_key in udp4_gro_receive
or udp6_gro_receive.

> > +	    NAPI_GRO_CB(skb)->is_flist) {
> >   		pp = call_gro_receive(udp_gro_receive_segment, head, skb);

udp_gro_receive_segment will check is_flist first and try to do
fraglisted UDP GRO. Can you check what I'm missing?

> >   		return pp;
> >   	}
> >
> 
> The second check for sk in "(sk && udp_sk(sk)->gro_enabled)" is
> redundant and can be dropped. You already verified it is present when
> you checked for !sk before the logical OR.
> 

Sorry, Alexander Duyck. I believe Alexander Lobakin will answer this.

> > -	if (!sk || NAPI_GRO_CB(skb)->encap_mark ||
> > +	if (NAPI_GRO_CB(skb)->encap_mark ||
> >   	    (skb->ip_summed != CHECKSUM_PARTIAL &&
> >   	     NAPI_GRO_CB(skb)->csum_cnt == 0 &&
> >   	     !NAPI_GRO_CB(skb)->csum_valid) ||
> >