Re: [PATCH bpf-next v11 05/10] libbpf: Add support for global percpu data

On 7/8/26 00:57, [email protected] wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Low] Dead code in percpu global data feature check
> --
> 
> --- Patch [5]: [PATCH bpf-next v11 05/10] libbpf: Add support for global percpu data ---
> commit ee97f8a8e25b5e9337024df3dd6f3a1aae4f6cdc
> Author: Leon Hwang <[email protected]>
> 
> libbpf: Add support for global percpu data
> 
> This commit adds support for global percpu data in libbpf by introducing a 
> new ".percpu" section. It updates the lightweight skeleton loader to use 
> BPF_F_ALL_CPUS when updating the percpu_array map and marks the mmaped data 
> as read-only after population.
> 
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index 514e4e9daa825..9f79a8e850fdb 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
> 
> [ ... ]
> 
>> @@ -5293,18 +5326,26 @@ static int
>>  bpf_object__populate_internal_map(struct bpf_object *obj, struct bpf_map *map)
>>  {
>>  	enum libbpf_map_type map_type = map->libbpf_type;
>> +	bool is_percpu = map_type == LIBBPF_MAP_PERCPU;
>> +	const __u64 update_flags = is_percpu ? BPF_F_ALL_CPUS : 0;
>>  	int err, zero = 0;
>>  	size_t mmap_sz;
>>  
>> +	if (is_percpu && !obj->gen_loader && !kernel_supports(obj, FEAT_PERCPU_DATA)) {
>> +		pr_warn("map '%s': kernel does not support percpu data.\n",
>> +			bpf_map__name(map));
>> +		return -EOPNOTSUPP;
>> +	}
>> +
> 
> [Severity: Low]
> Is this check reachable? 
> 
> Looking at bpf_object__create_maps(), if the kernel does not support
> FEAT_PERCPU_DATA, map->autocreate is set to false and the map processing
> loop continues early:
> 
> bpf_object__create_maps() {
>     ...
>     if (bpf_map__is_internal(map) && bpf_map__type(map) == BPF_MAP_TYPE_PERCPU_ARRAY &&
>         !kernel_supports(obj, FEAT_PERCPU_DATA))
>         map->autocreate = false;
> 
>     if (!map->autocreate) {
>         pr_debug("map '%s': skipped auto-creating...\n", map->name);
>         continue;
>     }
>     ...
> }
> 
> Since bpf_object__populate_internal_map() is called later in this same
> loop (after the continue), wouldn't the !kernel_supports() condition
> already be filtered out, making this warning dead code?
> 

True.

Will drop this warning.

And, update 'bpf_map__type(map) == BPF_MAP_TYPE_PERCPU_ARRAY' to
'map->libbpf_type == LIBBPF_MAP_PERCPU' in bpf_object__create_maps().

Thanks,
Leon