selftests/bpf: Prevent client connect before server bind in test_tc_tunnel.sh

[ Upstream commit f803bcf9208a2540acb4c32bdc3616673169f490 ]

In some systems, the netcat server can incur in delay to start listening.
When this happens, the test can randomly fail in various points.
This is an example error message:

   # ip gre none gso
   # encap 192.168.1.1 to 192.168.1.2, type gre, mac none len 2000
   # test basic connectivity
   # Ncat: Connection refused.

The issue stems from a race condition between the netcat client and server.
The test author had addressed this problem by implementing a sleep, which
I have removed in this patch.
This patch introduces a function capable of sleeping for up to two seconds.
However, it can terminate the waiting period early if the port is reported
to be listening.

Signed-off-by: Alessandro Carminati (Red Hat) <alessandro.carminati@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240314105911.213411-1-alessandro.carminati@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/tools/testing/selftests/bpf/test_tc_tunnel.sh b/tools/testing/selftests/bpf/test_tc_tunnel.sh
index 7c76b841b17bb72875da4e5802956eadba8bc0e3..21bde60c952307d4a9c7b88d3b4e444673ff8890 100755 (executable)
--- a/tools/testing/selftests/bpf/test_tc_tunnel.sh
+++ b/tools/testing/selftests/bpf/test_tc_tunnel.sh
@@ -71,7 +71,6 @@ cleanup() {
 server_listen() {
        ip netns exec "${ns2}" nc "${netcat_opt}" -l -p "${port}" > "${outfile}" &
        server_pid=$!
-       sleep 0.2
 }
 
 client_connect() {
@@ -92,6 +91,16 @@ verify_data() {
        fi
 }
 
+wait_for_port() {
+       for i in $(seq 20); do
+               if ip netns exec "${ns2}" ss ${2:--4}OHntl | grep -q "$1"; then
+                       return 0
+               fi
+               sleep 0.1
+       done
+       return 1
+}
+
 set -e
 
 # no arguments: automated test, run all
@@ -183,6 +192,7 @@ setup
 # basic communication works
 echo "test basic connectivity"
 server_listen
+wait_for_port ${port} ${netcat_opt}
 client_connect
 verify_data
 
@@ -194,6 +204,7 @@ ip netns exec "${ns1}" tc filter add dev veth1 egress \
        section "encap_${tuntype}_${mac}"
 echo "test bpf encap without decap (expect failure)"
 server_listen
+wait_for_port ${port} ${netcat_opt}
 ! client_connect
 
 if [[ "$tuntype" =~ "udp" ]]; then