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

[Anubhav Singh]

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 <will...@google.com>
Signed-off-by: Anubhav Singh <anubhavsin...@google.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