selftests/bpf: test_progs: fix client/server race in tcp_rtt

This is the same problem I found earlier in test_sockopt_inherit:
there is a race between server thread doing accept() and client
thread doing connect(). Let's explicitly synchronize them via
pthread conditional variable.

v2:
* don't exit from server_thread without signaling condvar,
  fixes possible issue where main() would wait forever (Andrii Nakryiko)

Fixes: b55873984dab ("selftests/bpf: test BPF_SOCK_OPS_RTT_CB")
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 19 insertions, 2 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/tcp_rtt.c b/tools/testing/selftests/bpf/prog_tests/tcp_rtt.c
index fdc0b3614a9e..a82da555b1b0 100644
--- a/tools/testing/selftests/bpf/prog_tests/tcp_rtt.c
+++ b/tools/testing/selftests/bpf/prog_tests/tcp_rtt.c
@@ -203,14 +203,24 @@ static int start_server(void)
         return fd;
 }
 
+static pthread_mutex_t server_started_mtx = PTHREAD_MUTEX_INITIALIZER;
+static pthread_cond_t server_started = PTHREAD_COND_INITIALIZER;
+
 static void *server_thread(void *arg)
 {
         struct sockaddr_storage addr;
         socklen_t len = sizeof(addr);
         int fd = *(int *)arg;
         int client_fd;
+        int err;
+
+        err = listen(fd, 1);
+
+        pthread_mutex_lock(&server_started_mtx);
+        pthread_cond_signal(&server_started);
+        pthread_mutex_unlock(&server_started_mtx);
 
-        if (CHECK_FAIL(listen(fd, 1)) < 0) {
+        if (CHECK_FAIL(err < 0)) {
                 perror("Failed to listed on socket");
                 return NULL;
         }
@@ -248,7 +258,14 @@ void test_tcp_rtt(void)
         if (CHECK_FAIL(server_fd < 0))
                 goto close_cgroup_fd;
 
-        pthread_create(&tid, NULL, server_thread, (void *)&server_fd);
+        if (CHECK_FAIL(pthread_create(&tid, NULL, server_thread,
+                                      (void *)&server_fd)))
+                goto close_cgroup_fd;
+
+        pthread_mutex_lock(&server_started_mtx);
+        pthread_cond_wait(&server_started, &server_started_mtx);
+        pthread_mutex_unlock(&server_started_mtx);
+
         CHECK_FAIL(run_test(cgroup_fd, server_fd));
         close(server_fd);
 close_cgroup_fd: