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Date:   Tue, 12 Jan 2021 21:16:17 +0000
From:   Alexander Lobakin <>
To:     "David S. Miller" <>,
        Jakub Kicinski <>
Cc:     Eric Dumazet <>,
        Edward Cree <>,
        Willem de Bruijn <>,
        Steffen Klassert <>,
        Alexey Kuznetsov <>,
        Hideaki YOSHIFUJI <>,,,
        Alexander Lobakin <>
Subject: [PATCH net-next] udp: allow forwarding of plain (non-fraglisted) UDP GRO packets

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.

Plain UDP GRO forwarding even shows better performance than fraglisted
UDP GRO in some cases due to not wasting one skbuff_head per every

Signed-off-by: Alexander Lobakin <>
 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;
-	if ((sk && udp_sk(sk)->gro_enabled) || NAPI_GRO_CB(skb)->is_flist) {
+	if (!sk || (sk && udp_sk(sk)->gro_enabled) ||
+	    NAPI_GRO_CB(skb)->is_flist) {
 		pp = call_gro_receive(udp_gro_receive_segment, head, skb);
 		return pp;
-	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) ||

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