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Date:   Tue, 28 May 2019 18:03:53 -0400
From:   Johannes Weiner <hannes@cmpxchg.org>
To:     Roman Gushchin <guro@fb.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, kernel-team@fb.com,
        Michal Hocko <mhocko@kernel.org>,
        Rik van Riel <riel@surriel.com>,
        Shakeel Butt <shakeelb@google.com>,
        Christoph Lameter <cl@linux.com>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        cgroups@vger.kernel.org, Waiman Long <longman@redhat.com>
Subject: Re: [PATCH v5 5/7] mm: rework non-root kmem_cache lifecycle
 management
Message-ID: <20190528220353.GC26614@cmpxchg.org>
References: <20190521200735.2603003-1-guro@fb.com>
 <20190521200735.2603003-6-guro@fb.com>
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On Tue, May 21, 2019 at 01:07:33PM -0700, Roman Gushchin wrote:
> +	arr = rcu_dereference(cachep->memcg_params.memcg_caches);
> +
> +	/*
> +	 * Make sure we will access the up-to-date value. The code updating
> +	 * memcg_caches issues a write barrier to match this (see
> +	 * memcg_create_kmem_cache()).
> +	 */
> +	memcg_cachep = READ_ONCE(arr->entries[kmemcg_id]);

READ_ONCE() isn't an SMP barrier, it just prevents compiler
muckery. This needs an explicit smp_rmb() to pair with the smp_wmb()
on the other side.

I realize you're only moving this code, but it would be good to fix
that up while you're there.