netdev - [PATCH net] selftests/net: fix out-of-order delivery of FIN in gro:tcp test

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Message-ID: <20251030055714.1553346-1-anubhavsinggh@google.com>
Date: Thu, 30 Oct 2025 05:57:14 +0000
From: Anubhav Singh <anubhavsinggh@...gle.com>
To: netdev@...r.kernel.org, linux-kselftest@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Willem de Bruijn <willemb@...gle.com>, Coco Li <lixiaoyan@...gle.com>, 
	Anubhav Singh <anubhavsinggh@...gle.com>
Subject: [PATCH net] selftests/net: fix out-of-order delivery of FIN in
 gro:tcp test

Due to the gro_sender sending data packets and FIN packets
in very quick succession, these are received almost simultaneously
by the gro_receiver. FIN packets are sometimes processed before the
data packets leading to intermittent (~1/100) test failures.

This change adds a delay of 100ms before sending FIN packets
in gro:tcp test to avoid the out-of-order delivery. The same
mitigation already exists for the gro:ip test.

Fixes: 7d1575014a63 ("selftests/net: GRO coalesce test")
Reviewed-by: Willem de Bruijn <willemb@...gle.com>
Signed-off-by: Anubhav Singh <anubhavsinggh@...gle.com>
---
 tools/testing/selftests/net/gro.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/tools/testing/selftests/net/gro.c b/tools/testing/selftests/net/gro.c
index 2b1d9f2b3e9e..3fa63bd85dea 100644
--- a/tools/testing/selftests/net/gro.c
+++ b/tools/testing/selftests/net/gro.c
@@ -989,6 +989,7 @@ static void check_recv_pkts(int fd, int *correct_payload,
 
 static void gro_sender(void)
 {
+	const int fin_delay_us = 100 * 1000;
 	static char fin_pkt[MAX_HDR_LEN];
 	struct sockaddr_ll daddr = {};
 	int txfd = -1;
@@ -1032,15 +1033,22 @@ static void gro_sender(void)
 		write_packet(txfd, fin_pkt, total_hdr_len, &daddr);
 	} else if (strcmp(testname, "tcp") == 0) {
 		send_changed_checksum(txfd, &daddr);
+		/* Adding sleep before sending FIN so that it is not
+		 * received prior to other packets.
+		 */
+		usleep(fin_delay_us);
 		write_packet(txfd, fin_pkt, total_hdr_len, &daddr);
 
 		send_changed_seq(txfd, &daddr);
+		usleep(fin_delay_us);
 		write_packet(txfd, fin_pkt, total_hdr_len, &daddr);
 
 		send_changed_ts(txfd, &daddr);
+		usleep(fin_delay_us);
 		write_packet(txfd, fin_pkt, total_hdr_len, &daddr);
 
 		send_diff_opt(txfd, &daddr);
+		usleep(fin_delay_us);
 		write_packet(txfd, fin_pkt, total_hdr_len, &daddr);
 	} else if (strcmp(testname, "ip") == 0) {
 		send_changed_ECN(txfd, &daddr);
-- 
2.51.1.851.g4ebd6896fd-goog