netdev - [PATCH net-next 4/5] net: gro: remove unnecessary df checks

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Message-Id: <20250814114030.7683-5-richardbgobert@gmail.com>
Date: Thu, 14 Aug 2025 13:40:29 +0200
From: Richard Gobert <richardbgobert@...il.com>
To: netdev@...r.kernel.org
Cc: davem@...emloft.net,
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	Richard Gobert <richardbgobert@...il.com>
Subject: [PATCH net-next 4/5] net: gro: remove unnecessary df checks

Currently, packets with fixed IDs will be merged only if their
don't-fragment bit is set. Merged packets are re-split into segments
before being fragmented, so the result is the same as if the packets
weren't merged to begin with.

Remove unnecessary don't-fragment checks.

Signed-off-by: Richard Gobert <richardbgobert@...il.com>
---
 include/net/gro.h                 | 5 ++---
 net/ipv4/af_inet.c                | 3 ---
 tools/testing/selftests/net/gro.c | 9 ++++-----
 3 files changed, 6 insertions(+), 11 deletions(-)

diff --git a/include/net/gro.h b/include/net/gro.h
index e7997a9fb30b..e3affb2e2ca8 100644
--- a/include/net/gro.h
+++ b/include/net/gro.h
@@ -448,17 +448,16 @@ static inline int inet_gro_flush(const struct iphdr *iph, const struct iphdr *ip
 	const u32 id2 = ntohl(*(__be32 *)&iph2->id);
 	const u16 ipid_offset = (id >> 16) - (id2 >> 16);
 	const u16 count = NAPI_GRO_CB(p)->count;
-	const u32 df = id & IP_DF;
 
 	/* All fields must match except length and checksum. */
-	if ((iph->ttl ^ iph2->ttl) | (iph->tos ^ iph2->tos) | (df ^ (id2 & IP_DF)))
+	if ((iph->ttl ^ iph2->ttl) | (iph->tos ^ iph2->tos) | ((id ^ id2) & IP_DF))
 		return true;
 
 	/* When we receive our second frame we can make a decision on if we
 	 * continue this flow as an atomic flow with a fixed ID or if we use
 	 * an incrementing ID.
 	 */
-	if (count == 1 && df && !ipid_offset)
+	if (count == 1 && !ipid_offset)
 		NAPI_GRO_CB(p)->ip_fixedid |= 1 << inner;
 
 	return ipid_offset ^ (count * !(NAPI_GRO_CB(p)->ip_fixedid & (1 << inner)));
diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 7f29b485009d..b4052cabdfc4 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1393,10 +1393,7 @@ struct sk_buff *inet_gso_segment(struct sk_buff *skb,
 
 	segs = ERR_PTR(-EPROTONOSUPPORT);
 
-	/* fixed ID is invalid if DF bit is not set */
 	fixedid = !!(skb_shinfo(skb)->gso_type & (SKB_GSO_TCP_FIXEDID_OUTER << encap));
-	if (fixedid && !(ip_hdr(skb)->frag_off & htons(IP_DF)))
-		goto out;
 
 	if (!skb->encapsulation || encap)
 		udpfrag = !!(skb_shinfo(skb)->gso_type & SKB_GSO_UDP);
diff --git a/tools/testing/selftests/net/gro.c b/tools/testing/selftests/net/gro.c
index d5824eadea10..3d4a82a2607c 100644
--- a/tools/testing/selftests/net/gro.c
+++ b/tools/testing/selftests/net/gro.c
@@ -670,7 +670,7 @@ static void send_flush_id_case(int fd, struct sockaddr_ll *daddr, int tcase)
 		iph2->id = htons(9);
 		break;
 
-	case 3: /* DF=0, Fixed - should not coalesce */
+	case 3: /* DF=0, Fixed - should coalesce */
 		iph1->frag_off &= ~htons(IP_DF);
 		iph1->id = htons(8);
 
@@ -1188,10 +1188,9 @@ static void gro_receiver(void)
 			correct_payload[0] = PAYLOAD_LEN * 2;
 			check_recv_pkts(rxfd, correct_payload, 1);
 
-			printf("DF=0, Fixed - should not coalesce: ");
-			correct_payload[0] = PAYLOAD_LEN;
-			correct_payload[1] = PAYLOAD_LEN;
-			check_recv_pkts(rxfd, correct_payload, 2);
+			printf("DF=0, Fixed - should coalesce: ");
+			correct_payload[0] = PAYLOAD_LEN * 2;
+			check_recv_pkts(rxfd, correct_payload, 1);
 
 			printf("DF=1, 2 Incrementing and one fixed - should coalesce only first 2 packets: ");
 			correct_payload[0] = PAYLOAD_LEN * 2;
-- 
2.36.1