Re: [PATCH v2] btf: warn but return no error for NULL btf from __register_btf_kfunc_id_set()

[Daniel Borkmann]

On 6/30/23 9:48 PM, SeongJae Park wrote:
> On Fri, 30 Jun 2023 16:53:38 +0200 Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
> > On 6/28/23 6:46 PM, 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@xxxxxxx>
> > > Link: https://lore.kernel.org/bpf/87y228q66f.fsf@xxxxxxxxxxxxxxxxxxxx/
> > > Suggested-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
> > > Link: https://lore.kernel.org/bpf/20220219082037.ow2kbq5brktf4f2u@apollo.legion/
> > > Fixes: c446fdacb10d ("bpf: fix register_btf_kfunc_id_set for !CONFIG_DEBUG_INFO_BTF")
> > > Cc: <stable@xxxxxxxxxxxxxxx> # 5.18.x
> > > Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
> > > Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> >
> > I presume this one is targeted at bpf (rather than bpf-next) tree, right?
>
> You're correct.  It's not urgent for us, but I would prefer it to be merged
> into all affected kernels as early as possible.

Ok, sounds good, bpf tree it is then.

> > > 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;
> > > -		}
> >
> > Why the above one needs to be changed? Do you also run into this case? vmlinux BTF
> > should be built-in in this case. I understand it's rather the one below for BTF +
> > modules instead, no?
>
> Again, you're correct.  This change is not really needed.  I was interpreting
> Kumar's suggestion merely into code without thinking about his real meaning,
> sorry.  I will restore this in the next spin.

Perfect, I think after your v3 respin it should be good to land.

Thanks,
Daniel