> On Feb 21, 2023, at 13:17, Roman Gushchin <roman.gushchin@xxxxxxxxx> wrote: > >> On Feb 20, 2023, at 3:06 PM, Shakeel Butt <shakeelb@xxxxxxxxxx> wrote: >> >> 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@xxxxxxxxx> >>> >>> 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. > > Needed for what? > > I mean it’s obviously not a big deal to put READ_ONCE()/WRITE_ONCE() here, but I struggle to imagine a scenario when it will make any difference. IMHO it’s easier to justify a proper atomic operation here, even if it’s most likely an overkill. > > My question is very simple: the commit log mentions “… to avoid concurrency problems”, so I wonder what problems are these. I think there is no difference in the assembly code between them in most cases. The only intention that I can think of is to avoid the potential complaint (data race) emitted by KCSAN. > > Also there are other similar cgroup interfaces without READ_ONCE()/WRITE_ONCE(). If we decide to fix, then we should fix all. Thanks. > > Thanks!
