Re: [PATCH bpf-next v2] selftests/bpf: Avoid flaky resize value test for percpu data

[Leon Hwang <leon.hwang@linux.dev>]

On 19/8/26 00:15, bot+bpf-ci@kernel.org wrote:
>> 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 5671c31085cd..2b69290bcc3e 100644
>> --- a/tools/testing/selftests/bpf/prog_tests/global_data_init.c
>> +++ b/tools/testing/selftests/bpf/prog_tests/global_data_init.c
> 
> [ ... ]
> 
>> @@ -236,6 +223,57 @@ static void test_global_percpu_data_lskel(void)
>>  	test_global_percpu_data_lskel__destroy(lskel);
>>  }
>>
>> +#define PAGE_SIZE 4096
>> +
>> +static void test_global_percpu_data_map_resize(void)
>> +{
>> +	const __u32 desired_sz = sysconf(_SC_PAGE_SIZE) * 2;
>> +	struct test_global_percpu_data *skel;
>> +	const int arr_value = -1;
>> +	struct bpf_map *map;
>> +	int err, prog_fd;
>> +	size_t data_sz;
>> +
>> +	if (sysconf(_SC_PAGE_SIZE) != PAGE_SIZE) {
>> +		test__skip();
>> +		return;
>> +	}
>> +
>> +	skel = test_global_percpu_data__open();
>> +	if (!ASSERT_OK_PTR(skel, "test_global_percpu_data__open"))
>> +		return;
>> +
>> +	map = skel->maps.percpu_arr;
>> +	skel->percpu_arr->arr[0] = arr_value;
>> +	err = bpf_map__set_value_size(map, desired_sz);
> 
> This isn't a bug, but since the guard above already pins the page size to
> 4096, would `const __u32 desired_sz = PAGE_SIZE * 2;` read more directly

Will change to 'PAGE_SIZE * 2' if the next revision is needed.

> here - and is the unguarded `#define PAGE_SIZE 4096` preferable to the
> `#ifndef PAGE_SIZE` form used in sockopt.c?

No. PAGE_SIZE must be 4096 here.

> 
>> +	if (!ASSERT_OK(err, "bpf_map__set_value_size"))
>> +		goto out;
>> +	if (!ASSERT_EQ(bpf_map__value_size(map), desired_sz, "bpf_map__value_size"))
>> +		goto out;
>> +	if (!ASSERT_NEQ(bpf_map__btf_value_type_id(map), 0, "bpf_map__btf_value_type_id"))
>> +		goto out;
>> +
>> +	skel->percpu_arr = bpf_map__initial_value(map, &data_sz);
>> +	if (!ASSERT_EQ(data_sz, desired_sz, "data_sz"))
>> +		goto out;
>> +	if (!ASSERT_OK_PTR(skel->percpu_arr, "skel->percpu_arr"))
>> +		goto out;
> 
> This isn't a bug, but would it read more consistently with
> test_global_percpu_data_init() to check ASSERT_OK_PTR(skel->percpu_arr)
> before ASSERT_EQ(data_sz, desired_sz)? The block this replaces checked
> pointer-then-size, and the surviving test_global_percpu_data_init() at the
> same file still does pointer-then-size.

Unnecessary to keep consistent for their order. This is a really minor
readability concern.

Thanks,
Leon