selftests: net: Add FIN_ACK processing order related latency spike test

This commit adds a test for FIN_ACK process races related reconnection
latency spike issues. The issue has described and solved by the
previous commit ("tcp: Reduce SYN resend delay if a suspicous ACK is
received").

The test program is configured with a server and a client process. The
server creates and binds a socket to a port that dynamically allocated,
listen on it, and start a infinite loop. Inside the loop, it accepts
connection, reads 4 bytes from the socket, and closes the connection.
The client is constructed as an infinite loop. Inside the loop, it
creates a socket with LINGER and NODELAY option, connect to the server,
send 4 bytes data, try read some data from server. After the read()
returns, it measure the latency from the beginning of this loop to this
point and if the latency is larger than 1 second (spike), print a
message.

Reviewed-by: Eric Dumazet <[e-mail]>
Signed-off-by: SeongJae Park <[e-mail]>
Signed-off-by: Jakub Kicinski <[e-mail]>

tools/testing/selftests/net/.gitignore

···
 so_txtime
 tcp_fastopen_backup_key
 nettest
+fin_ack_lat

tools/testing/selftests/net/Makefile

···
 TEST_PROGS += udpgro_bench.sh udpgro.sh test_vxlan_under_vrf.sh reuseport_addr_any.sh
 TEST_PROGS += test_vxlan_fdb_changelink.sh so_txtime.sh ipv6_flowlabel.sh
 TEST_PROGS += tcp_fastopen_backup_key.sh fcnal-test.sh l2tp.sh traceroute.sh
+TEST_PROGS += fin_ack_lat.sh
 TEST_PROGS_EXTENDED := in_netns.sh
 TEST_GEN_FILES =  socket nettest
 TEST_GEN_FILES += psock_fanout psock_tpacket msg_zerocopy reuseport_addr_any
···
 TEST_GEN_FILES += udpgso udpgso_bench_tx udpgso_bench_rx ip_defrag
 TEST_GEN_FILES += so_txtime ipv6_flowlabel ipv6_flowlabel_mgr
 TEST_GEN_FILES += tcp_fastopen_backup_key
+TEST_GEN_FILES += fin_ack_lat
 TEST_GEN_PROGS = reuseport_bpf reuseport_bpf_cpu reuseport_bpf_numa
 TEST_GEN_PROGS += reuseport_dualstack reuseaddr_conflict tls
 

tools/testing/selftests/net/fin_ack_lat.c

···
+// SPDX-License-Identifier: GPL-2.0
+
+#include <arpa/inet.h>
+#include <errno.h>
+#include <error.h>
+#include <netinet/in.h>
+#include <netinet/tcp.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/socket.h>
+#include <sys/time.h>
+#include <unistd.h>
+
+static int child_pid;
+
+static unsigned long timediff(struct timeval s, struct timeval e)
+{
+	unsigned long s_us, e_us;
+
+	s_us = s.tv_sec * 1000000 + s.tv_usec;
+	e_us = e.tv_sec * 1000000 + e.tv_usec;
+	if (s_us > e_us)
+		return 0;
+	return e_us - s_us;
+}
+
+static void client(int port)
+{
+	int sock = 0;
+	struct sockaddr_in addr, laddr;
+	socklen_t len = sizeof(laddr);
+	struct linger sl;
+	int flag = 1;
+	int buffer;
+	struct timeval start, end;
+	unsigned long lat, sum_lat = 0, nr_lat = 0;
+
+	while (1) {
+		gettimeofday(&start, NULL);
+
+		sock = socket(AF_INET, SOCK_STREAM, 0);
+		if (sock < 0)
+			error(-1, errno, "socket creation");
+
+		sl.l_onoff = 1;
+		sl.l_linger = 0;
+		if (setsockopt(sock, SOL_SOCKET, SO_LINGER, &sl, sizeof(sl)))
+			error(-1, errno, "setsockopt(linger)");
+
+		if (setsockopt(sock, IPPROTO_TCP, TCP_NODELAY,
+					&flag, sizeof(flag)))
+			error(-1, errno, "setsockopt(nodelay)");
+
+		addr.sin_family = AF_INET;
+		addr.sin_port = htons(port);
+
+		if (inet_pton(AF_INET, "127.0.0.1", &addr.sin_addr) <= 0)
+			error(-1, errno, "inet_pton");
+
+		if (connect(sock, (struct sockaddr *)&addr, sizeof(addr)) < 0)
+			error(-1, errno, "connect");
+
+		send(sock, &buffer, sizeof(buffer), 0);
+		if (read(sock, &buffer, sizeof(buffer)) == -1)
+			error(-1, errno, "waiting read");
+
+		gettimeofday(&end, NULL);
+		lat = timediff(start, end);
+		sum_lat += lat;
+		nr_lat++;
+		if (lat < 100000)
+			goto close;
+
+		if (getsockname(sock, (struct sockaddr *)&laddr, &len) == -1)
+			error(-1, errno, "getsockname");
+		printf("port: %d, lat: %lu, avg: %lu, nr: %lu\n",
+				ntohs(laddr.sin_port), lat,
+				sum_lat / nr_lat, nr_lat);
+close:
+		fflush(stdout);
+		close(sock);
+	}
+}
+
+static void server(int sock, struct sockaddr_in address)
+{
+	int accepted;
+	int addrlen = sizeof(address);
+	int buffer;
+
+	while (1) {
+		accepted = accept(sock, (struct sockaddr *)&address,
+				(socklen_t *)&addrlen);
+		if (accepted < 0)
+			error(-1, errno, "accept");
+
+		if (read(accepted, &buffer, sizeof(buffer)) == -1)
+			error(-1, errno, "read");
+		close(accepted);
+	}
+}
+
+static void sig_handler(int signum)
+{
+	kill(SIGTERM, child_pid);
+	exit(0);
+}
+
+int main(int argc, char const *argv[])
+{
+	int sock;
+	int opt = 1;
+	struct sockaddr_in address;
+	struct sockaddr_in laddr;
+	socklen_t len = sizeof(laddr);
+
+	if (signal(SIGTERM, sig_handler) == SIG_ERR)
+		error(-1, errno, "signal");
+
+	sock = socket(AF_INET, SOCK_STREAM, 0);
+	if (sock < 0)
+		error(-1, errno, "socket");
+
+	if (setsockopt(sock, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT,
+				&opt, sizeof(opt)) == -1)
+		error(-1, errno, "setsockopt");
+
+	address.sin_family = AF_INET;
+	address.sin_addr.s_addr = INADDR_ANY;
+	/* dynamically allocate unused port */
+	address.sin_port = 0;
+
+	if (bind(sock, (struct sockaddr *)&address, sizeof(address)) < 0)
+		error(-1, errno, "bind");
+
+	if (listen(sock, 3) < 0)
+		error(-1, errno, "listen");
+
+	if (getsockname(sock, (struct sockaddr *)&laddr, &len) == -1)
+		error(-1, errno, "getsockname");
+
+	fprintf(stderr, "server port: %d\n", ntohs(laddr.sin_port));
+	child_pid = fork();
+	if (!child_pid)
+		client(ntohs(laddr.sin_port));
+	else
+		server(sock, laddr);
+
+	return 0;
+}

tools/testing/selftests/net/fin_ack_lat.sh

···
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Test latency spikes caused by FIN/ACK handling race.
+
+set +x
+set -e
+
+tmpfile=$(mktemp /tmp/fin_ack_latency.XXXX.log)
+
+cleanup() {
+	kill $(pidof fin_ack_lat)
+	rm -f $tmpfile
+}
+
+trap cleanup EXIT
+
+do_test() {
+	RUNTIME=$1
+
+	./fin_ack_lat | tee $tmpfile &
+	PID=$!
+
+	sleep $RUNTIME
+	NR_SPIKES=$(wc -l $tmpfile | awk '{print $1}')
+	if [ $NR_SPIKES -gt 0 ]
+	then
+		echo "FAIL: $NR_SPIKES spikes detected"
+		return 1
+	fi
+	return 0
+}
+
+do_test "30"
+echo "test done"