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From:   Roman Gushchin <guro@fb.com>
To:     Shakeel Butt <shakeelb@google.com>
CC:     Andrew Morton <akpm@linux-foundation.org>,
        Linux MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Kernel Team <Kernel-team@fb.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Waiman Long <longman@redhat.com>
Subject: Re: [PATCH v6 01/10] mm: add missing smp read barrier on getting
 memcg kmem_cache pointer
Thread-Topic: [PATCH v6 01/10] mm: add missing smp read barrier on getting
 memcg kmem_cache pointer
Thread-Index: AQHVG0i1Qy6vvrJhnUaeUsu3v8l0raaMeYMAgADUCYA=
Date:   Wed, 5 Jun 2019 17:14:02 +0000
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On Tue, Jun 04, 2019 at 09:35:02PM -0700, Shakeel Butt wrote:
> On Tue, Jun 4, 2019 at 7:45 PM Roman Gushchin <guro@fb.com> wrote:
> >
> > Johannes noticed that reading the memcg kmem_cache pointer in
> > cache_from_memcg_idx() is performed using READ_ONCE() macro,
> > which doesn't implement a SMP barrier, which is required
> > by the logic.
> >
> > Add a proper smp_rmb() to be paired with smp_wmb() in
> > memcg_create_kmem_cache().
> >
> > The same applies to memcg_create_kmem_cache() itself,
> > which reads the same value without barriers and READ_ONCE().
> >
> > Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
> > Signed-off-by: Roman Gushchin <guro@fb.com>
>=20
> Reviewed-by: Shakeel Butt <shakeelb@google.com>
>=20
> This seems like independent to the series. Shouldn't this be Cc'ed stable=
?

It is independent, but let's keep it here to avoid merge conflicts.

It has been so for a long time, and nobody complained, so I'm not sure
if we really need a stable backport. Do you have a different opinion?

Thank you!