Re: [PATCH v10 2/5] sched: CGroup tagging interface for core scheduling

[Josh Don]

On Thu, Feb 4, 2021 at 6:02 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Fri, Jan 22, 2021 at 08:17:01PM -0500, Joel Fernandes (Google) wrote:
>
> > +#ifdef CONFIG_SCHED_DEBUG
> > +     /* Read the group cookie. */
> > +     {
> > +             .name = "core_group_cookie",
> > +             .flags = CFTYPE_NOT_ON_ROOT,
> > +             .read_u64 = cpu_core_group_cookie_read_u64,
> > +     },
> > +#endif
>
> > +#ifdef CONFIG_SCHED_DEBUG
> > +     /* Read the group cookie. */
> > +     {
> > +             .name = "core_group_cookie",
> > +             .flags = CFTYPE_NOT_ON_ROOT,
> > +             .read_u64 = cpu_core_group_cookie_read_u64,
> > +     },
> > +#endif
>
> AFAICT this leaks kernel pointers. IIRC that was a bad thing.

For that matter, we're also exposing the cookie pointer in
/proc/$pid/sched. Currently these are used by the selftests to
validate that two tasks are/aren't sharing.  If this poses a risk, we
can rework to avoid exposing the actual pointers.