selftests/bpf: Fix test_run logic in fexit_stress.c

In the commit da00d2f1 ("bpf: Add test ops for BPF_PROG_TYPE_TRACING"),
the bpf_fentry_test1 function was moved into bpf_prog_test_run_tracing(),
which is the test_run function of the tracing BPF programs.

Thus calling 'bpf_prog_test_run_opts(filter_fd, &topts)' will not trigger
bpf_fentry_test1 function as filter_fd is a sk_filter BPF program.

Fix it by replacing filter_fd with fexit_fd in the bpf_prog_test_run_opts()
function.

Fixes: da00d2f1 ("bpf: Add test ops for BPF_PROG_TYPE_TRACING")
Signed-off-by: Yuntao Wang <ytcoode@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220521151329.648013-1-ytcoode@gmail.com

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

@@ -7,11 +7,9 @@
 
 void serial_test_fexit_stress(void)
 {
-	char test_skb[128] = {};
 	int fexit_fd[CNT] = {};
 	int link_fd[CNT] = {};
-	char error[4096];
-	int err, i, filter_fd;
+	int err, i;
 
 	const struct bpf_insn trace_program[] = {
 		BPF_MOV64_IMM(BPF_REG_0, 0),
@@ -20,25 +18,9 @@ void serial_test_fexit_stress(void)
 
 	LIBBPF_OPTS(bpf_prog_load_opts, trace_opts,
 		.expected_attach_type = BPF_TRACE_FEXIT,
-		.log_buf = error,
-		.log_size = sizeof(error),
 	);
 
-	const struct bpf_insn skb_program[] = {
-		BPF_MOV64_IMM(BPF_REG_0, 0),
-		BPF_EXIT_INSN(),
-	};
-
-	LIBBPF_OPTS(bpf_prog_load_opts, skb_opts,
-		.log_buf = error,
-		.log_size = sizeof(error),
-	);
-
-	LIBBPF_OPTS(bpf_test_run_opts, topts,
-		.data_in = test_skb,
-		.data_size_in = sizeof(test_skb),
-		.repeat = 1,
-	);
+	LIBBPF_OPTS(bpf_test_run_opts, topts);
 
 	err = libbpf_find_vmlinux_btf_id("bpf_fentry_test1",
 					 trace_opts.expected_attach_type);
@@ -58,15 +40,9 @@ void serial_test_fexit_stress(void)
 			goto out;
 	}
 
-	filter_fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, NULL, "GPL",
-				  skb_program, sizeof(skb_program) / sizeof(struct bpf_insn),
-				  &skb_opts);
-	if (!ASSERT_GE(filter_fd, 0, "test_program_loaded"))
-		goto out;
+	err = bpf_prog_test_run_opts(fexit_fd[0], &topts);
+	ASSERT_OK(err, "bpf_prog_test_run_opts");
 
-	err = bpf_prog_test_run_opts(filter_fd, &topts);
-	close(filter_fd);
-	CHECK_FAIL(err);
 out:
 	for (i = 0; i < CNT; i++) {
 		if (link_fd[i])