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From:   Shakeel Butt <shakeelb@google.com>
Date:   Wed, 5 Jun 2019 12:51:14 -0700
Message-ID: <CALvZod6Cu+Uyy-Jp-er0Kz9dwLhmb5KO0XP3X55PVcSx4A4w3g@mail.gmail.com>
Subject: Re: [PATCH v6 01/10] mm: add missing smp read barrier on getting
 memcg kmem_cache pointer
To:     Roman Gushchin <guro@fb.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>
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On Wed, Jun 5, 2019 at 10:14 AM Roman Gushchin <guro@fb.com> wrote:
>
> 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>
> >
> > Reviewed-by: Shakeel Butt <shakeelb@google.com>
> >
> > 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?
>

Nah, it's fine as it is.