Re: [PATCH bpf-next v10 9/9] selftests/bpf: Verify bpf_iter for global percpu data

["Emil Tsalapatis" <emil@etsalapatis.com>]

On Wed Jul 15, 2026 at 11:32 AM EDT, Leon Hwang wrote:
> Add a test to verify that it is OK to iter the percpu_array map used for
> global percpu data.
>
> Signed-off-by: Leon Hwang <leon.hwang@linux.dev>

Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>

> ---
>  .../bpf/prog_tests/global_data_init.c         | 52 +++++++++++++++++++
>  .../bpf/progs/test_global_percpu_data.c       | 25 +++++++++
>  2 files changed, 77 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/global_data_init.c b/tools/testing/selftests/bpf/prog_tests/global_data_init.c
> index 598b7dde6581..e5a40ea36ee7 100644
> --- a/tools/testing/selftests/bpf/prog_tests/global_data_init.c
> +++ b/tools/testing/selftests/bpf/prog_tests/global_data_init.c
> @@ -283,6 +283,56 @@ static void test_global_percpu_data_verifier_log(void)
>  	RUN_TESTS(test_global_percpu_data);
>  }
>  
> +static void test_global_percpu_data_iter(void)
> +{
> +	DECLARE_LIBBPF_OPTS(bpf_iter_attach_opts, opts);
> +	struct test_global_percpu_data *skel;
> +	union bpf_iter_link_info linfo = {};
> +	struct bpf_link *link = NULL;
> +	int fd, num_cpus, len, err;
> +	char buf[16];
> +
> +	num_cpus = libbpf_num_possible_cpus();
> +	if (!ASSERT_GT(num_cpus, 0, "libbpf_num_possible_cpus"))
> +		return;
> +
> +	skel = test_global_percpu_data__open();
> +	if (!ASSERT_OK_PTR(skel, "test_global_percpu_data__open"))
> +		return;
> +
> +	skel->rodata->num_cpus = num_cpus;
> +	skel->rodata->offsetof_num = offsetof(struct test_global_percpu_data__percpu, struct_data);
> +	skel->rodata->offsetof_num += sizeof(skel->percpu->struct_data) - sizeof(int);
> +	skel->rodata->elem_sz = roundup(sizeof(struct test_global_percpu_data__percpu), 8);
> +	skel->percpu->struct_data.nums[6] = 0xc0de;
> +
> +	err = test_global_percpu_data__load(skel);
> +	if (!ASSERT_OK(err, "test_global_percpu_data__load"))
> +		goto out;
> +
> +	linfo.map.map_fd = bpf_map__fd(skel->maps.percpu);
> +	opts.link_info = &linfo;
> +	opts.link_info_len = sizeof(linfo);
> +	link = bpf_program__attach_iter(skel->progs.dump_percpu_data, &opts);
> +	if (!ASSERT_OK_PTR(link, "bpf_program__attach_iter"))
> +		goto out;
> +
> +	fd = bpf_iter_create(bpf_link__fd(link));
> +	if (!ASSERT_GE(fd, 0, "bpf_iter_create"))
> +		goto out;
> +
> +	while ((len = read(fd, buf, sizeof(buf))) > 0)
> +		do { } while (0);
> +	ASSERT_EQ(len, 0, "read iter");
> +	ASSERT_TRUE(skel->bss->run_iter, "run_iter");
> +	ASSERT_EQ(skel->bss->percpu_data_sum, 0xc0de * num_cpus, "percpu_data_sum");
> +
> +	close(fd);
> +out:
> +	bpf_link__destroy(link);
> +	test_global_percpu_data__destroy(skel);
> +}
> +
>  void test_global_percpu_data(void)
>  {
>  	if (!feat_supported(NULL, FEAT_PERCPU_DATA)) {
> @@ -299,4 +349,6 @@ void test_global_percpu_data(void)
>  	if (test__start_subtest("rdonly_direct_write"))
>  		test_global_percpu_data_rdonly_direct_write();
>  	test_global_percpu_data_verifier_log();
> +	if (test__start_subtest("iter"))
> +		test_global_percpu_data_iter();
>  }
> diff --git a/tools/testing/selftests/bpf/progs/test_global_percpu_data.c b/tools/testing/selftests/bpf/progs/test_global_percpu_data.c
> index b852a0b07508..8b1f625017d1 100644
> --- a/tools/testing/selftests/bpf/progs/test_global_percpu_data.c
> +++ b/tools/testing/selftests/bpf/progs/test_global_percpu_data.c
> @@ -53,4 +53,29 @@ int verifier_snprintf(void *ctx)
>  	return 0;
>  }
>  
> +volatile const __u32 num_cpus = 0;
> +volatile const int offsetof_num;
> +volatile const int elem_sz;
> +__u32 percpu_data_sum = 0;
> +bool run_iter = false;
> +
> +SEC("iter/bpf_map_elem")
> +__auxiliary
> +int dump_percpu_data(struct bpf_iter__bpf_map_elem *ctx)
> +{
> +	void *pptr = ctx->value;
> +	int i;
> +
> +	if (!pptr)
> +		return 0;
> +
> +	run_iter = true;
> +
> +	for (i = 0; i < num_cpus; i++) {
> +		percpu_data_sum += *(int *) (pptr + offsetof_num);
> +		pptr += elem_sz;
> +	}
> +	return 0;
> +}
> +
>  char _license[] SEC("license") = "GPL";