Re: [PATCH] bpf: Add env_type_is_resolved() in front of env_stack_push() in btf_resolve()

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Tue, Sep 7, 2021 at 3:37 PM Martin KaFai Lau <kafai@fb.com> wrote:
>
> On Thu, Sep 02, 2021 at 06:37:13AM +0000, jiasheng wrote:
> > We have found that in the complied files env_stack_push()
> > appear more than 10 times, and under at least 90% circumstances
> > that env_type_is_resolved() and env_stack_push() appear in pairs.
> > For example, they appear together in the btf_modifier_resolve()
> > of the file complie from 'kernel/bpf/btf.c'.
> > But we have found that in the btf_resolve(), there is only
> > env_stack_push() instead of the pair.
> > Therefore, we consider that the env_type_is_resolved()
> > might be forgotten.
> It does not justify a change like this just because
> one of its usage looks different and then concluded that
> it _might_ be forgotten.
>
> Does it have a bug or not?  If there is, please
> provide an explanation on how to reproduce it first.
>

Both places that call btf_resolve() check that env_type_is_resolved()
first, so there is no issue here.

> >
> > Signed-off-by: jiasheng <jiasheng@iscas.ac.cn>
> > ---
> >  kernel/bpf/btf.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > index f982a9f0..454c249 100644
> > --- a/kernel/bpf/btf.c
> > +++ b/kernel/bpf/btf.c
> > @@ -4002,7 +4002,8 @@ static int btf_resolve(struct btf_verifier_env *env,
> >       int err = 0;
> >
> >       env->resolve_mode = RESOLVE_TBD;
> > -     env_stack_push(env, t, type_id);
> > +     if (env_type_is_resolved(env, type_id))
> > +             env_stack_push(env, t, type_id);
> >       while (!err && (v = env_stack_peak(env))) {
> >               env->log_type_id = v->type_id;
> >               err = btf_type_ops(v->t)->resolve(env, v);
> > --
> > 2.7.4
> >