linux-kernel - Re: [PATCH] mm: change memcg->oom_group access with atomic operations

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Message-ID: <20230220230624.lkobqeagycx7bi7p@google.com>
Date:   Mon, 20 Feb 2023 23:06:24 +0000
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Roman Gushchin <roman.gushchin@...ux.dev>
Cc:     Yue Zhao <findns94@...il.com>, linux-mm@...ck.org,
        akpm@...ux-foundation.org, hannes@...xchg.org, mhocko@...nel.org,
        muchun.song@...ux.dev, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: change memcg->oom_group access with atomic operations

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@...il.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.