VSOCK: add full barrier between test cases

See code comment for details.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/vsock/util.c

@@ -161,10 +161,24 @@ void run_tests(const struct test_case *test_cases,
 		printf("%s...", test_cases[i].name);
 		fflush(stdout);
 
-		if (opts->mode == TEST_MODE_CLIENT)
+		if (opts->mode == TEST_MODE_CLIENT) {
+			/* Full barrier before executing the next test.  This
+			 * ensures that client and server are executing the
+			 * same test case.  In particular, it means whoever is
+			 * faster will not see the peer still executing the
+			 * last test.  This is important because port numbers
+			 * can be used by multiple test cases.
+			 */
+			control_expectln("NEXT");
+			control_writeln("NEXT");
+
 			run = test_cases[i].run_client;
-		else
+		} else {
+			control_writeln("NEXT");
+			control_expectln("NEXT");
+
 			run = test_cases[i].run_server;
+		}
 
 		if (run)
 			run(opts);