linux-kernel - Re: [PATCH] btf: warn but return no error for NULL btf from __register_btf_kfunc_id

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Date:   Tue, 27 Jun 2023 18:20:39 +0200
From:   Jiri Olsa <olsajiri@...il.com>
To:     SeongJae Park <sj@...nel.org>
Cc:     martin.lau@...ux.dev, ast@...nel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Alexander Egorenkov <Alexander.Egorenkov@....com>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH] btf: warn but return no error for NULL btf from
 __register_btf_kfunc_id_set()

On Mon, Jun 26, 2023 at 06:11:20PM +0000, SeongJae Park wrote:
> __register_btf_kfunc_id_set() assumes .BTF to be part of the module's
> .ko file if CONFIG_DEBUG_INFO_BTF is enabled.  If that's not the case,
> the function prints an error message and return an error.  As a result,
> such modules cannot be loaded.
> 
> However, the section could be stripped out during a build process.  It
> would be better to let the modules loaded, because their basic
> functionalities have no problem[1], though the BTF functionalities will
> not be supported.  Make the function to lower the level of the message
> from error to warn, and return no error.
> 
> [1] https://lore.kernel.org/bpf/20220219082037.ow2kbq5brktf4f2u@apollo.legion/
> 
> Reported-by: Alexander Egorenkov <Alexander.Egorenkov@....com>
> Link: https://lore.kernel.org/bpf/87y228q66f.fsf@oc8242746057.ibm.com/
> Suggested-by: Kumar Kartikeya Dwivedi <memxor@...il.com>
> Link: https://lore.kernel.org/bpf/20220219082037.ow2kbq5brktf4f2u@apollo.legion/
> Fixes: dee872e124e8 ("bpf: Populate kfunc BTF ID sets in struct btf")

should it be this one in Fixes instead?
  c446fdacb10d bpf: fix register_btf_kfunc_id_set for !CONFIG_DEBUG_INFO_BTF

other than that looks good

Acked-by: Jiri Olsa <jolsa@...nel.org>

jirka

> Cc: <stable@...r.kernel.org> # 5.17.x
> Signed-off-by: SeongJae Park <sj@...nel.org>
> ---
>  kernel/bpf/btf.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 6b682b8e4b50..d683f034996f 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -7848,14 +7848,10 @@ static int __register_btf_kfunc_id_set(enum btf_kfunc_hook hook,
>  
>  	btf = btf_get_module_btf(kset->owner);
>  	if (!btf) {
> -		if (!kset->owner && IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) {
> -			pr_err("missing vmlinux BTF, cannot register kfuncs\n");
> -			return -ENOENT;
> -		}
> -		if (kset->owner && IS_ENABLED(CONFIG_DEBUG_INFO_BTF_MODULES)) {
> -			pr_err("missing module BTF, cannot register kfuncs\n");
> -			return -ENOENT;
> -		}
> +		if (!kset->owner && IS_ENABLED(CONFIG_DEBUG_INFO_BTF))
> +			pr_warn("missing vmlinux BTF, cannot register kfuncs\n");
> +		if (kset->owner && IS_ENABLED(CONFIG_DEBUG_INFO_BTF_MODULES))
> +			pr_warn("missing module BTF, cannot register kfuncs\n");
>  		return 0;
>  	}
>  	if (IS_ERR(btf))
> -- 
> 2.25.1
> 
>