Re: [PATCH 6.4 000/292] 6.4.5-rc1 review

[Alexander Potapenko <glider@google.com>]

On Tue, Jul 25, 2023 at 3:39 PM Naresh Kamboju
<naresh.kamboju@linaro.org> wrote:
>
> On Tue, 25 Jul 2023 at 17:22, Alexander Potapenko <glider@google.com> wrote:
> >
> > On Tue, Jul 25, 2023 at 11:59 AM Alexander Potapenko <glider@google.com> wrote:
> > >
> > > On Mon, Jul 24, 2023 at 2:10 PM Naresh Kamboju
> > > <naresh.kamboju@linaro.org> wrote:
> > > >
> > > > On Mon, 24 Jul 2023 at 15:50, Alexander Potapenko <glider@google.com> wrote:
> > > > >
> > > > > On Sat, Jul 22, 2023 at 6:37 PM Linus Torvalds
> > > > > <torvalds@linux-foundation.org> wrote:
> > > > > >
> > > > > > [ Removed the stable reviewers, bringing in the kfence people ]
> > > > > >
> > > > > > See
> > > > > >
> > > > > >   https://lore.kernel.org/lkml/CA+G9fYvgy22wiY=c3wLOrCM6o33636abhtEynXhJkqxJh4ca0A@mail.gmail.com/
> > > > > >
> > > > > > for the original report. The warning was introduced in 8f0b36497303
> > > > > > ("mm: kfence: fix objcgs vector allocation"), and Google doesn't find
> > > > > > any other cases of this.
> > > > > >
> > > > > > Anybody?
> > > > > >
> > > > > >                     Linus
> > > > > >
> > > > >

Muchun, any chance you know under what circumstances a KFENCE object
has its meta->objcg set to a non-NULL value?
It seems to be a quite rare case, and I've only seen it in live
radix_tree_node objects.
Since the check here:
https://elixir.bootlin.com/linux/latest/source/mm/kfence/core.c#L1097
ensures that this value is NULL when the object is freed, where is the
code that is supposed to zero it?
Could there be a race somewhere?