linux-kernel - Re: [PATCH bpf-next v12 5/7] bpf: Add BPF_F_CPU and BPF_F_ALL_CPUS flags support for percpu_cgroup

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Message-Id: <edd9991150f1456a7868025636825d7cf7595802e4a2fe405900c53fc1799ed8@mail.kernel.org>
Date: Wed, 26 Nov 2025 15:11:38 +0000 (UTC)
From: bot+bpf-ci@...nel.org
To: leon.hwang@...ux.dev,bpf@...r.kernel.org
Cc: ast@...nel.org,andrii@...nel.org,daniel@...earbox.net,jolsa@...nel.org,yonghong.song@...ux.dev,song@...nel.org,eddyz87@...il.com,dxu@...uu.xyz,deso@...teo.net,martin.lau@...ux.dev,john.fastabend@...il.com,kpsingh@...nel.org,sdf@...ichev.me,haoluo@...gle.com,shuah@...nel.org,kerneljasonxing@...il.com,chen.dylane@...ux.dev,willemb@...gle.com,paul.chaignon@...il.com,a.s.protopopov@...il.com,memxor@...il.com,yatsenko@...a.com,tklauser@...tanz.ch,leon.hwang@...ux.dev,kernel-patches-bot@...com,linux-kernel@...r.kernel.org,linux-kselftest@...r.kernel.org,ast@...nel.org,andrii@...nel.org,daniel@...earbox.net,martin.lau@...nel.org,eddyz87@...il.com,yonghong.song@...ux.dev,clm@...a.com,ihor.solodrai@...ux.dev
Subject: Re: [PATCH bpf-next v12 5/7] bpf: Add BPF_F_CPU and BPF_F_ALL_CPUS flags support for percpu_cgroup_storage maps

> diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h
> index aedf573bd..013f4db99 100644
> --- a/include/linux/bpf-cgroup.h
> +++ b/include/linux/bpf-cgroup.h

[ ... ]

> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index f79d2ae27..9e756db5e 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h

[ ... ]

> diff --git a/kernel/bpf/local_storage.c b/kernel/bpf/local_storage.c
> index 2ab4b60ff..1ccbf28b2 100644
> --- a/kernel/bpf/local_storage.c
> +++ b/kernel/bpf/local_storage.c
> @@ -180,7 +180,7 @@ static long cgroup_storage_update_elem(struct bpf_map *map, void *key,
>  }
>
>  int bpf_percpu_cgroup_storage_copy(struct bpf_map *_map, void *key,
> -				   void *value)
> +				   void *value, u64 map_flags)
>  {
>  	struct bpf_cgroup_storage_map *map = map_to_storage(_map);
>  	struct bpf_cgroup_storage *storage;
> @@ -198,11 +198,17 @@ int bpf_percpu_cgroup_storage_copy(struct bpf_map *_map, void *key,
>  	 * access 'value_size' of them, so copying rounded areas
>  	 * will not leak any kernel data
>  	 */
> +	if (map_flags & BPF_F_CPU) {
> +		cpu = map_flags >> 32;
> +		copy_map_value(_map, value, per_cpu_ptr(storage->percpu_buf, cpu));
> +		goto unlock;
> +	}

Should check_and_init_map_value() be called here after copy_map_value()?

The similar implementations in bpf_percpu_array_copy() and
bpf_percpu_hash_copy() both call check_and_init_map_value() after
copying a single CPU's value when BPF_F_CPU is set:

  bpf_percpu_array_copy():
    if (map_flags & BPF_F_CPU) {
        cpu = map_flags >> 32;
        copy_map_value(map, value, per_cpu_ptr(pptr, cpu));
        check_and_init_map_value(map, value);
        goto unlock;
    }

  bpf_percpu_hash_copy():
    if (map_flags & BPF_F_CPU) {
        cpu = map_flags >> 32;
        copy_map_value(map, value, per_cpu_ptr(pptr, cpu));
        check_and_init_map_value(map, value);
        goto out;
    }

The check_and_init_map_value() call initializes special BTF fields
(timers, kptrs, etc.) when copying map values to userspace. Without it,
these fields might not be properly initialized if percpu_cgroup_storage
map values contain such fields.

>  	size = round_up(_map->value_size, 8);
>  	for_each_possible_cpu(cpu) {
>  		copy_map_value_long(_map, value + off, per_cpu_ptr(storage->percpu_buf, cpu));
>  		off += size;
>  	}
> +unlock:
>  	rcu_read_unlock();
>  	return 0;
>  }

[ ... ]


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/19708012130