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

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Message-ID: <20190605164227.GB12453@cmpxchg.org>
Date:   Wed, 5 Jun 2019 12:42:27 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Roman Gushchin <guro@...com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@...com,
        Shakeel Butt <shakeelb@...gle.com>,
        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 07:44:45PM -0700, Roman Gushchin 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>

Acked-by: Johannes Weiner <hannes@...xchg.org>