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charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: utyfnj6o6ti1sdcp8puqunp3kq14yaa1 X-Rspam-User: X-Rspamd-Queue-Id: 420EA180030 X-Rspamd-Server: rspam06 X-HE-Tag: 1676998897-23622 X-HE-Meta: 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 StB/0xFZ rFIjbFaSdtPqs2k241evR0FHh49Ppol9YV4l0sLhgSA6Wsycun77xI6vEk2+RuuOq7xpS3GPok1FUPFKI4u7GqFotchfuu/jH/5f35FIFR/h0J5nJQiROCn4IdbYMz+Bo6NvliB1WCOY1v5qtd0gPh7M4YbDimcUg3lqhYWQg7AAEtMqs2BzD1YKaLBr5J1oeC4TMk19IPM7F9VvESnE9NFuuofZwCeMzTR5B8DqOcy8RrSAaEwU1tA5buqo6pnDr8ry0g2eCd02jAhxjoQ1TtrgtwDSSjmnFDsZEPX3AfqX6V3otEr/j0LMavOorFLRyuggzG9XC9zy1GEQpCDvAGcNHUWpZjTntfPzQZTBOf49zfDNAYIEsPM/2QGi2Ol17bXOGV+w0G1l9vcPcCDy4gTNEgFhqL+eaPrq/EQRcqfhOJRuNwrqSGA/SAQMGYilQ8oRd9xIyz8akqO0= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000003, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Feb 21, 2023 at 1:17 PM Roman Gushchin w= rote: > > > On Feb 20, 2023, at 3:06 PM, Shakeel Butt wrote: > > > > =EF=BB=BFOn 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. > > Needed for what? > > I mean it=E2=80=99s obviously not a big deal to put READ_ONCE()/WRITE_ONC= E() here, but I struggle to imagine a scenario when it will make any differ= ence. IMHO it=E2=80=99s easier to justify a proper atomic operation here, e= ven if it=E2=80=99s most likely an overkill. > > My question is very simple: the commit log mentions =E2=80=9C=E2=80=A6 to= avoid concurrency problems=E2=80=9D, so I wonder what problems are these. Thanks for your watching! This topic is found in code review by coincidence, so no real issues recorded for now. I checked other read/write callbacks about other knobs, most of them use READ_ONCE/WRITE_ONCE on the user setting variable. Actually I am curious as well why this interface doesn't use READ_ONCE/WRITE_ONCE, is there any other synchronization mechanism I didn't notice yet? > > Also there are other similar cgroup interfaces without READ_ONCE()/WRITE_= ONCE(). > > Thanks!