Re: [PATCH bpf-next v3 3/4] selftests/bpf: Add selftest for attaching tracing programs to functions in deny list

[Yonghong Song <yonghong.song@linux.dev>]

On 7/22/25 8:34 AM, KaFai Wan wrote:
> The result:
>
>   $ tools/testing/selftests/bpf/test_progs -t tracing_failure/tracing_deny
>   #468/3   tracing_failure/tracing_deny:OK
>   #468     tracing_failure:OK
>   Summary: 1/1 PASSED, 0 SKIPPED, 0 FAILED
>
> Signed-off-by: KaFai Wan <kafai.wan@linux.dev>

LGTM but see a nit below.

Acked-by: Yonghong Song <yonghong.song@linux.dev>

> ---
>   .../bpf/prog_tests/tracing_failure.c          | 33 +++++++++++++++++++
>   .../selftests/bpf/progs/tracing_failure.c     |  6 ++++
>   2 files changed, 39 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/tracing_failure.c b/tools/testing/selftests/bpf/prog_tests/tracing_failure.c
> index a222df765bc3..140fb0d175cf 100644
> --- a/tools/testing/selftests/bpf/prog_tests/tracing_failure.c
> +++ b/tools/testing/selftests/bpf/prog_tests/tracing_failure.c
> @@ -28,10 +28,43 @@ static void test_bpf_spin_lock(bool is_spin_lock)
>   	tracing_failure__destroy(skel);
>   }
>   
> +static void test_tracing_deny(void)
> +{
> +	struct tracing_failure *skel;
> +	char log_buf[256];
> +	int btf_id, err;
> +
> +	/* migrate_disable depends on CONFIG_SMP */
> +	btf_id = libbpf_find_vmlinux_btf_id("migrate_disable", BPF_TRACE_FENTRY);
> +	if (btf_id <= 0) {
> +		test__skip();
> +		return;
> +	}

There is a discussion about inlining migrate_disable(). See
   https://lore.kernel.org/bpf/CAADnVQ+Afov4E=9t=3M=zZmO9z4ZqT6imWD5xijDHshTf3J=RA@mail.gmail.com/

Maybe trying to find a different function? Otherwise, if migrate_disable
is inlined and this test will become useless.

> +
> +	skel = tracing_failure__open();
> +	if (!ASSERT_OK_PTR(skel, "tracing_failure__open"))
> +		return;
> +
> +	bpf_program__set_autoload(skel->progs.tracing_deny, true);
> +	bpf_program__set_log_buf(skel->progs.tracing_deny, log_buf, sizeof(log_buf));
> +
> +	err = tracing_failure__load(skel);
> +	if (!ASSERT_ERR(err, "tracing_failure__load"))
> +		goto out;
> +
> +	ASSERT_HAS_SUBSTR(log_buf,
> +			  "Attaching tracing programs to function 'migrate_disable' is rejected.",
> +			  "log_buf");
> +out:
> +	tracing_failure__destroy(skel);
> +}
> +
>   void test_tracing_failure(void)
>   {
>   	if (test__start_subtest("bpf_spin_lock"))
>   		test_bpf_spin_lock(true);
>   	if (test__start_subtest("bpf_spin_unlock"))
>   		test_bpf_spin_lock(false);
> +	if (test__start_subtest("tracing_deny"))
> +		test_tracing_deny();
>   }
> diff --git a/tools/testing/selftests/bpf/progs/tracing_failure.c b/tools/testing/selftests/bpf/progs/tracing_failure.c
> index d41665d2ec8c..dfa152e8194e 100644
> --- a/tools/testing/selftests/bpf/progs/tracing_failure.c
> +++ b/tools/testing/selftests/bpf/progs/tracing_failure.c
> @@ -18,3 +18,9 @@ int BPF_PROG(test_spin_unlock, struct bpf_spin_lock *lock)
>   {
>   	return 0;
>   }
> +
> +SEC("?fentry/migrate_disable")
> +int BPF_PROG(tracing_deny)
> +{
> +	return 0;
> +}