linux-kernel - Re: [PATCH bpf-next] bpf: btf: don't log ignored BTF mismatches

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Date:   Wed, 9 Nov 2022 08:45:07 -0800
From:   Yonghong Song <yhs@...a.com>
To:     Connor O'Brien <connoro@...gle.com>, bpf@...r.kernel.org
Cc:     Martin KaFai Lau <martin.lau@...ux.dev>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next] bpf: btf: don't log ignored BTF mismatches



On 11/8/22 6:41 PM, Connor O'Brien wrote:
> Enabling CONFIG_MODULE_ALLOW_BTF_MISMATCH is an indication that BTF
> mismatches are expected and module loading should proceed
> anyway. Logging with pr_warn() on every one of these "benign"
> mismatches creates unnecessary noise when many such modules are
> loaded. Instead, limit logging to the case where a BTF mismatch
> actually prevents a module form loading.
> 
> Signed-off-by: Connor O'Brien <connoro@...gle.com>
> ---
>   kernel/bpf/btf.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 5579ff3a5b54..406370487413 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -7190,11 +7190,12 @@ static int btf_module_notify(struct notifier_block *nb, unsigned long op,
>   		}
>   		btf = btf_parse_module(mod->name, mod->btf_data, mod->btf_data_size);
>   		if (IS_ERR(btf)) {
> -			pr_warn("failed to validate module [%s] BTF: %ld\n",
> -				mod->name, PTR_ERR(btf));

I think such warning still useful even with 
CONFIG_MODULE_ALLOW_BTF_MISMATCH.
Can we use pr_warn_ratelimited instead of pr_warn in the above to
avoid excessive warnings?

>   			kfree(btf_mod);
> -			if (!IS_ENABLED(CONFIG_MODULE_ALLOW_BTF_MISMATCH))
> +			if (!IS_ENABLED(CONFIG_MODULE_ALLOW_BTF_MISMATCH)) {
> +				pr_warn("failed to validate module [%s] BTF: %ld\n",
> +					mod->name, PTR_ERR(btf));
>   				err = PTR_ERR(btf);
> +			}
>   			goto out;
>   		}
>   		err = btf_alloc_id(btf);