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

Shakeel Butt
2023-02-20T23:06:31Z

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.