selftests/bpf: Fix potential unreleased lock

This lock is not released if the program
return at the patched branch.

Signed-off-by: Chengfeng Ye <cyeaa@connect.ust.hk>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210827074140.118671-1-cyeaa@connect.ust.hk

tools/testing/selftests/bpf/prog_tests/sockopt_inherit.c

@@ -195,8 +195,10 @@ static void run_test(int cgroup_fd)
 
 	pthread_mutex_lock(&server_started_mtx);
 	if (CHECK_FAIL(pthread_create(&tid, NULL, server_thread,
-				      (void *)&server_fd)))
+				      (void *)&server_fd))) {
+		pthread_mutex_unlock(&server_started_mtx);
 		goto close_server_fd;
+	}
 	pthread_cond_wait(&server_started, &server_started_mtx);
 	pthread_mutex_unlock(&server_started_mtx);