linux-kernel - Re: [PATCH v6 01/10] mm: add missing smp read barrier on getting memcg kmem

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Message-ID: <20190605171355.GA10098@tower.DHCP.thefacebook.com>
Date:   Wed, 5 Jun 2019 17:14:02 +0000
From:   Roman Gushchin <guro@...com>
To:     Shakeel Butt <shakeelb@...gle.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Waiman Long <longman@...hat.com>
Subject: Re: [PATCH v6 01/10] mm: add missing smp read barrier on getting
 memcg kmem_cache pointer

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@...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@...xchg.org>
> > Signed-off-by: Roman Gushchin <guro@...com>
> 
> Reviewed-by: Shakeel Butt <shakeelb@...gle.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?

Thank you!