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From:   Josh Don <joshdon@google.com>
Date:   Thu, 4 Feb 2021 19:55:12 -0800
Message-ID: <CABk29NsmV=6fstw3qEPpEb5Zw9K6hpQSASE5yS68Zjj9_HDkcg@mail.gmail.com>
Subject: Re: [PATCH v10 2/5] sched: CGroup tagging interface for core scheduling
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     "Joel Fernandes (Google)" <joel@joelfernandes.org>,
        Nishanth Aravamudan <naravamudan@digitalocean.com>,
        Julien Desfossez <jdesfossez@digitalocean.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Vineeth Pillai <viremana@linux.microsoft.com>,
        Aaron Lu <aaron.lwe@gmail.com>,
        Aubrey Li <aubrey.intel@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel <linux-kernel@vger.kernel.org>, mingo@kernel.org,
        torvalds@linux-foundation.org, fweisbec@gmail.com,
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        Valentin Schneider <valentin.schneider@arm.com>,
        Mel Gorman <mgorman@techsingularity.net>,
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On Thu, Feb 4, 2021 at 6:02 AM Peter Zijlstra <peterz@infradead.org> 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.