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

[Yonghong Song <yhs@meta.com>]

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@google.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);