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From: Shakeel Butt To: Kuniyuki Iwashima Cc: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Neal Cardwell , Paolo Abeni , Willem de Bruijn , Matthieu Baerts , Mat Martineau , Johannes Weiner , Michal Hocko , Roman Gushchin , Andrew Morton , Michal =?utf-8?Q?Koutn=C3=BD?= , Tejun Heo , Simon Horman , Geliang Tang , Muchun Song , Mina Almasry , Kuniyuki Iwashima , netdev@vger.kernel.org, mptcp@lists.linux.dev, cgroups@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v5 net-next 01/10] mptcp: Fix up subflow's memcg when CONFIG_SOCK_CGROUP_DATA=n. Message-ID: <3x5m5rvbvtnta6lqyyx6k3uew4zhg5nxt2wmadkpi5t6tlsko6@peltw6axwvkg> References: <20250815201712.1745332-1-kuniyu@google.com> <20250815201712.1745332-2-kuniyu@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250815201712.1745332-2-kuniyu@google.com> X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: 38B214000C X-Stat-Signature: 4yowbcgsmnae1zujuf6eaxfn99sp9ikz X-HE-Tag: 1755300703-797190 X-HE-Meta: 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 3+9MJTUP 6cK9EZnjnmfgWfU0VVA+NnVCUpFwNqs1jDPUxiU6Yt3EeRbLrsp69+PRlReFvsNsY19D7F8cVOOLPzF03JAHQbZhdAjOuVG1TT0yQNqATcl41Py9LYnQ6y01Js0h0JB5B9nEArnAjokEQVIFRohU1k4uT8VmuiKK78ka7ZEJ6IrDLmgnEqJUML6Dd6zSrpnoXLo27aAafP9ChbIit5dCxwuO189DzdrMP8miGy/90UliKmx1TkR90MmLzegGoCLwT+Z1ymgSGoA/6V9OpevkxEepJHBPD8iO73SDfhgd7QTk19fE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Aug 15, 2025 at 08:16:09PM +0000, Kuniyuki Iwashima wrote: > When sk_alloc() allocates a socket, mem_cgroup_sk_alloc() sets > sk->sk_memcg based on the current task. > > MPTCP subflow socket creation is triggered from userspace or > an in-kernel worker. > > In the latter case, sk->sk_memcg is not what we want. So, we fix > it up from the parent socket's sk->sk_memcg in mptcp_attach_cgroup(). > > Although the code is placed under #ifdef CONFIG_MEMCG, it is buried > under #ifdef CONFIG_SOCK_CGROUP_DATA. > > The two configs are orthogonal. If CONFIG_MEMCG is enabled without > CONFIG_SOCK_CGROUP_DATA, the subflow's memory usage is not charged > correctly. > > Let's move the code out of the wrong ifdef guard. > > Note that sk->sk_memcg is freed in sk_prot_free() and the parent > sk holds the refcnt of memcg->css here, so we don't need to use > css_tryget(). > > Fixes: 3764b0c5651e3 ("mptcp: attach subflow socket to parent cgroup") > Signed-off-by: Kuniyuki Iwashima > Reviewed-by: Eric Dumazet > Acked-by: Matthieu Baerts (NGI0) Acked-by: Shakeel Butt