Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 3 May 2023 17:06:51 +0000
In-Reply-To: <20230502160839.361544-2-roman.gushchin@linux.dev>
Mime-Version: 1.0
References: <20230502160839.361544-1-roman.gushchin@linux.dev> <20230502160839.361544-2-roman.gushchin@linux.dev>
Message-ID: <20230503170651.cw5omegmm3piumxf@google.com>
Subject: Re: [PATCH v2 2/2] mm: memcg: use READ_ONCE()/WRITE_ONCE() to access stock->cached
From:   Shakeel Butt <shakeelb@google.com>
To:     Roman Gushchin <roman.gushchin@linux.dev>
Cc:     linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Muchun Song <muchun.song@linux.dev>,
        linux-kernel@vger.kernel.org, Dmitry Vyukov <dvyukov@google.com>,
        Yosry Ahmed <yosryahmed@google.com>
Content-Type: text/plain; charset="us-ascii"
Precedence: bulk

On Tue, May 02, 2023 at 09:08:39AM -0700, Roman Gushchin wrote:
> A memcg pointer in the percpu stock can be accessed by drain_all_stock()
> from another cpu in a lockless way.
> In theory it might lead to an issue, similar to the one which has been
> discovered with stock->cached_objcg, where the pointer was zeroed
> between the check for being NULL and dereferencing.
> In this case the issue is unlikely a real problem, but to make it
> bulletproof and similar to stock->cached_objcg, let's annotate all
> accesses to stock->cached with READ_ONCE()/WTRITE_ONCE().
> 
> Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: Yosry Ahmed <yosryahmed@google.com>
> Cc: Shakeel Butt <shakeelb@google.com>

Acked-by: Shakeel Butt <shakeelb@google.com>