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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 v4 net-next 01/10] mptcp: Fix up subflow's memcg when CONFIG_SOCK_CGROUP_DATA=n. Message-ID: References: <20250814200912.1040628-1-kuniyu@google.com> <20250814200912.1040628-2-kuniyu@google.com> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250814200912.1040628-2-kuniyu@google.com> X-Migadu-Flow: FLOW_OUT On Thu, Aug 14, 2025 at 08:08:33PM +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 wrap sock_create_kern() for subflow with set_active_memcg() > using the parent sk->sk_memcg. > > Fixes: 3764b0c5651e3 ("mptcp: attach subflow socket to parent cgroup") > Suggested-by: Michal Koutný > Signed-off-by: Kuniyuki Iwashima > --- > mm/memcontrol.c | 5 ++++- > net/mptcp/subflow.c | 11 +++-------- > 2 files changed, 7 insertions(+), 9 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 8dd7fbed5a94..450862e7fd7a 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -5006,8 +5006,11 @@ void mem_cgroup_sk_alloc(struct sock *sk) > if (!in_task()) > return; > > + memcg = current->active_memcg; > + Use active_memcg() instead of current->active_memcg and do before the !in_task() check. Basically something like following: memcg = active_memcg(); /* Do not associate the sock with unrelated interrupted task's memcg. */ if (!in_task() && !memcg) return; > rcu_read_lock(); > - memcg = mem_cgroup_from_task(current); > + if (likely(!memcg)) > + memcg = mem_cgroup_from_task(current); > if (mem_cgroup_is_root(memcg)) > goto out; > if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && !memcg1_tcpmem_active(memcg)) > diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c > index 3f1b62a9fe88..a4809054ea6c 100644 > --- a/net/mptcp/subflow.c > +++ b/net/mptcp/subflow.c > @@ -1717,14 +1717,6 @@ static void mptcp_attach_cgroup(struct sock *parent, struct sock *child) > /* only the additional subflows created by kworkers have to be modified */ > if (cgroup_id(sock_cgroup_ptr(parent_skcd)) != > cgroup_id(sock_cgroup_ptr(child_skcd))) { > -#ifdef CONFIG_MEMCG > - struct mem_cgroup *memcg = parent->sk_memcg; > - > - mem_cgroup_sk_free(child); > - if (memcg && css_tryget(&memcg->css)) > - child->sk_memcg = memcg; > -#endif /* CONFIG_MEMCG */ > - > cgroup_sk_free(child_skcd); > *child_skcd = *parent_skcd; > cgroup_sk_clone(child_skcd); > @@ -1757,6 +1749,7 @@ int mptcp_subflow_create_socket(struct sock *sk, unsigned short family, > { > struct mptcp_subflow_context *subflow; > struct net *net = sock_net(sk); > + struct mem_cgroup *memcg; > struct socket *sf; > int err; > > @@ -1766,7 +1759,9 @@ int mptcp_subflow_create_socket(struct sock *sk, unsigned short family, > if (unlikely(!sk->sk_socket)) > return -EINVAL; > > + memcg = set_active_memcg(sk->sk_memcg); > err = sock_create_kern(net, family, SOCK_STREAM, IPPROTO_TCP, &sf); > + set_active_memcg(memcg); > if (err) > return err; > > -- > 2.51.0.rc1.163.g2494970778-goog >