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Mon, 20 Feb 2023 15:06:27 -0800 (PST) Date: Mon, 20 Feb 2023 23:06:24 +0000 In-Reply-To: Mime-Version: 1.0 References: <20230220151638.1371-1-findns94@gmail.com> Message-ID: <20230220230624.lkobqeagycx7bi7p@google.com> Subject: Re: [PATCH] mm: change memcg->oom_group access with atomic operations From: Shakeel Butt To: Roman Gushchin Cc: Yue Zhao , linux-mm@kvack.org, akpm@linux-foundation.org, hannes@cmpxchg.org, mhocko@kernel.org, muchun.song@linux.dev, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="us-ascii" X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: DF968180013 X-Rspam-User: X-Stat-Signature: a6pfo3twew8p7f15o7qtxybkh8hsnuwb X-HE-Tag: 1676934387-77768 X-HE-Meta: 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 u9yxVEjQ 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000005, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Feb 20, 2023 at 01:09:44PM -0800, Roman Gushchin wrote: > On Mon, Feb 20, 2023 at 11:16:38PM +0800, Yue Zhao wrote: > > The knob for cgroup v2 memory controller: memory.oom.group > > will be read and written simultaneously by user space > > programs, thus we'd better change memcg->oom_group access > > with atomic operations to avoid concurrency problems. > > > > Signed-off-by: Yue Zhao > > Hi Yue! > > I'm curious, have any seen any real issues which your patch is solving? > Can you, please, provide a bit more details. > IMHO such details are not needed. oom_group is being accessed concurrently and one of them can be a write access. At least READ_ONCE/WRITE_ONCE is needed here. Most probably syzbot didn't catch this race because it does not know about the memory.oom.group interface.