Date:   Mon, 20 Feb 2023 23:06:24 +0000
In-Reply-To: <Y/PhmEPc/qYeZ52T@P9FQF9L96D>
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References: <20230220151638.1371-1-findns94@gmail.com> <Y/PhmEPc/qYeZ52T@P9FQF9L96D>
Message-ID: <20230220230624.lkobqeagycx7bi7p@google.com>
Subject: Re: [PATCH] mm: change memcg->oom_group access with atomic operations
From:   Shakeel Butt <shakeelb@google.com>
To:     Roman Gushchin <roman.gushchin@linux.dev>
Cc:     Yue Zhao <findns94@gmail.com>, 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
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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 <findns94@gmail.com>
> 
> 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.