Re: [PATCH bpf-next v7 4/4] selftests/bpf: Test re-attachment fix for bpf_tracing_prog_attach

[Jiri Olsa <olsajiri@gmail.com>]

On Fri, Dec 08, 2023 at 07:55:56PM +0100, Dmitrii Dolgov wrote:
> Add a test case to verify the fix for "prog->aux->dst_trampoline and
> tgt_prog is NULL" branch in bpf_tracing_prog_attach. The sequence of
> events:
> 
> 1. load rawtp program
> 2. load fentry program with rawtp as target_fd
> 3. create tracing link for fentry program with target_fd = 0
> 4. repeat 3
> 
> Signed-off-by: Dmitrii Dolgov <9erthalion6@gmail.com>
> ---
>  .../bpf/prog_tests/recursive_attach.c         | 48 +++++++++++++++++++
>  .../bpf/progs/fentry_recursive_target.c       | 11 +++++
>  2 files changed, 59 insertions(+)
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/recursive_attach.c b/tools/testing/selftests/bpf/prog_tests/recursive_attach.c
> index 7248d0661ee9..6296bcf95481 100644
> --- a/tools/testing/selftests/bpf/prog_tests/recursive_attach.c
> +++ b/tools/testing/selftests/bpf/prog_tests/recursive_attach.c
> @@ -67,3 +67,51 @@ void test_recursive_fentry_attach(void)
>  			fentry_recursive__destroy(tracing_chain[i]);
>  	}
>  }
> +
> +/*
> + * Test that a tracing prog reattachment (when we land in
> + * "prog->aux->dst_trampoline and tgt_prog is NULL" branch in
> + * bpf_tracing_prog_attach) does not lead to a crash due to missing attach_btf
> + */
> +void test_fentry_attach_btf_presence(void)
> +{
> +	struct fentry_recursive_target *target_skel = NULL;
> +	struct fentry_recursive *tracing_skel = NULL;
> +	struct bpf_program *prog;
> +	int err, link_fd, tgt_prog_fd;
> +
> +	target_skel = fentry_recursive_target__open_and_load();
> +	if (!ASSERT_OK_PTR(target_skel, "fentry_recursive_target__open_and_load"))
> +		goto close_prog;
> +
> +	tracing_skel = fentry_recursive__open();
> +	if (!ASSERT_OK_PTR(tracing_skel, "fentry_recursive__open"))
> +		goto close_prog;
> +
> +	prog = tracing_skel->progs.recursive_attach;
> +	tgt_prog_fd = bpf_program__fd(target_skel->progs.fentry_target);
> +	err = bpf_program__set_attach_target(prog, tgt_prog_fd, "fentry_target");
> +	if (!ASSERT_OK(err, "bpf_program__set_attach_target"))
> +		goto close_prog;
> +
> +	err = fentry_recursive__load(tracing_skel);
> +	if (!ASSERT_OK(err, "fentry_recursive__load"))
> +		goto close_prog;
> +
> +	LIBBPF_OPTS(bpf_link_create_opts, link_opts);

we don't need link_opts, you can pass NULL to below bpf_link_create call

> +
> +	link_fd = bpf_link_create(bpf_program__fd(tracing_skel->progs.recursive_attach),
> +							  0, BPF_TRACE_FENTRY, &link_opts);

wrong indentation

> +	if (!ASSERT_GE(link_fd, 0, "link_fd"))
> +		goto close_prog;
> +
> +	fentry_recursive__detach(tracing_skel);
> +
> +	err = fentry_recursive__attach(tracing_skel);
> +	if (!ASSERT_ERR(err, "fentry_recursive__attach"))
> +		goto close_prog;

no need to call goto in here, let's just have ASSERT_ERR without the if

> +
> +close_prog:
> +	fentry_recursive_target__destroy(target_skel);
> +	fentry_recursive__destroy(tracing_skel);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/fentry_recursive_target.c b/tools/testing/selftests/bpf/progs/fentry_recursive_target.c
> index b6fb8ebd598d..f812d2de0c3c 100644
> --- a/tools/testing/selftests/bpf/progs/fentry_recursive_target.c
> +++ b/tools/testing/selftests/bpf/progs/fentry_recursive_target.c
> @@ -18,3 +18,14 @@ int BPF_PROG(test1, int a)
>  	test1_result = a == 1;
>  	return 0;
>  }
> +
> +/*
> + * Dummy bpf prog for testing attach_btf presence when attaching an fentry
> + * program.
> + */
> +SEC("raw_tp/sys_enter")
> +int BPF_PROG(fentry_target, struct pt_regs *regs, long id)
> +{
> +	test1_result = id == 1;

please remove test1_result

thanks,
jirka

> +	return 0;
> +}
> -- 
> 2.41.0
>