selftests/bpf: Fix reorder of attachment in mixed mprog test

Martin reported that on his local dev machine the test_tc_chain_mixed() fails as
"test_tc_chain_mixed:FAIL:seen_tc5 unexpected seen_tc5: actual 1 != expected 0".

However, when running in a more isolated setup (qemu in particular), it works fine
for him. The reason is that there is a small race-window where seen_tc5 could turn
into true given we first attach legacy tc, and then tcx. Fix it by swapping the
order of attachment.

Fixes: ccd9a8b ("selftests/bpf: Add various more tcx test cases")
Reported-by: Martin KaFai Lau <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>

Author: borkmann

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

@@ -1624,17 +1624,17 @@ static void test_tc_chain_mixed(int target)
 	if (!ASSERT_OK(err, "bpf_tc_hook_create"))
 		goto cleanup;
 
-	tc_opts.prog_fd = bpf_program__fd(skel->progs.tc5);
-	err = bpf_tc_attach(&tc_hook, &tc_opts);
-	if (!ASSERT_OK(err, "bpf_tc_attach"))
-		goto cleanup;
-
 	link = bpf_program__attach_tcx(skel->progs.tc6, loopback, &optl);
 	if (!ASSERT_OK_PTR(link, "link_attach"))
 		goto cleanup;
 
 	skel->links.tc6 = link;
 
+	tc_opts.prog_fd = bpf_program__fd(skel->progs.tc5);
+	err = bpf_tc_attach(&tc_hook, &tc_opts);
+	if (!ASSERT_OK(err, "bpf_tc_attach"))
+		goto cleanup;
+
 	assert_mprog_count(target, 1);
 
 	ASSERT_OK(system(ping_cmd), ping_cmd);

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

@@ -2303,17 +2303,17 @@ static void test_tc_chain_mixed(int target)
 	if (!ASSERT_OK(err, "bpf_tc_hook_create"))
 		goto cleanup;
 
-	tc_opts.prog_fd = fd2;
-	err = bpf_tc_attach(&tc_hook, &tc_opts);
-	if (!ASSERT_OK(err, "bpf_tc_attach"))
-		goto cleanup_hook;
-
 	err = bpf_prog_attach_opts(fd3, loopback, target, &opta);
 	if (!ASSERT_EQ(err, 0, "prog_attach"))
-		goto cleanup_filter;
+		goto cleanup_hook;
 
 	detach_fd = fd3;
 
+	tc_opts.prog_fd = fd2;
+	err = bpf_tc_attach(&tc_hook, &tc_opts);
+	if (!ASSERT_OK(err, "bpf_tc_attach"))
+		goto cleanup_filter;
+
 	assert_mprog_count(target, 1);
 
 	ASSERT_OK(system(ping_cmd), ping_cmd);