Re: [PATCH bpf-next v5 3/9] libbpf: Probe percpu data feature

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] The feature probe `probe_kern_percpu_data` unconditionally logs a warning and returns a negative error code when `bpf_map_create` fails, leading to duplicate spurious warnings on unprivileged or older kernels.
--

commit 18fee21f57e1b2a2407c8fad87c4a91712ba5351
Author: Leon Hwang <leon.hwang@linux.dev>
Subject: libbpf: Probe percpu data feature

This commit adds a dedicated feature probe to libbpf to reliably distinguish
kernels that support global percpu data from those that do not. This allows
libbpf to make capability decisions early.

> diff --git a/tools/lib/bpf/features.c b/tools/lib/bpf/features.c
> index b7e388f99d0bb..ef9581c113035 100644
> --- a/tools/lib/bpf/features.c
> +++ b/tools/lib/bpf/features.c
> @@ -620,6 +620,38 @@ static int probe_bpf_syscall_common_attrs(int token_fd)
>  	return probe_sys_bpf_ext();
>  }
>  
> +static int probe_kern_percpu_data(int token_fd)
> +{
> +	struct bpf_insn insns[] = {
> +		BPF_LD_MAP_VALUE(BPF_REG_1, 0, 0),
> +		BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, 0),
> +		BPF_EXIT_INSN(),
> +	};
> +	LIBBPF_OPTS(bpf_map_create_opts, map_opts,
> +		.token_fd = token_fd,
> +		.map_flags = token_fd ? BPF_F_TOKEN_FD : 0,
> +	);
> +	LIBBPF_OPTS(bpf_prog_load_opts, prog_opts,
> +		.token_fd = token_fd,
> +		.prog_flags = token_fd ? BPF_F_TOKEN_FD : 0,
> +	);
> +	int ret, map, insn_cnt = ARRAY_SIZE(insns);
> +
> +	map = bpf_map_create(BPF_MAP_TYPE_PERCPU_ARRAY, "libbpf_percpu", sizeof(int), 8, 1,
> +			     &map_opts);
> +	if (map < 0) {
> +		pr_warn("Error in %s(): %s. Couldn't create simple percpu_array map.\n",
> +			__func__, errstr(map));
> +		return map;
> +	}

[Severity: Low]
Does this unconditional warning and negative return value cause log spam on
older kernels or for unprivileged users?

When bpf_map_create() fails, returning the negative error code causes
feat_supported() to log a second "Detection of kernel ... support failed"
warning. Returning 0 instead would correctly signal that the feature is
missing without the additional log output, similar to how other probes
handle expected failures.

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260608145113.65857-1-leon.hwang@linux.dev?part=3