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

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Message-Id: <20230627163750.81178-1-sj@kernel.org>
Date:   Tue, 27 Jun 2023 16:37:50 +0000
From:   SeongJae Park <sj@...nel.org>
To:     Jiri Olsa <olsajiri@...il.com>
Cc:     SeongJae Park <sj@...nel.org>, 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()

Hi Jiri,

On Tue, 27 Jun 2023 18:20:39 +0200 Jiri Olsa <olsajiri@...il.com> wrote:

> 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

The commit c446fdacb10d was trying to fix commit dee872e124e8, which this patch
is claiming to fix, by relaxing the check.  Nevertheless, it seems the check
need to further relaxed, and therefore I wrote this patch.

For the reason, I was thinking this patch is directly fixing c446fdacb10d, but
is also fixing a problem originally introduced by dee872e124e8.   Nevertheless,
as the dee872e124e8 also has the Fixes tag, I think your suggestion makes
sense. 

I will fix so in the next spin.

> 
> other than that looks good
> 
> Acked-by: Jiri Olsa <jolsa@...nel.org>

Thank you, I will also add this to the next version of this patch :)


Thanks,
SJ

> 
> 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
> > 
> >