Re: [PATCH v4 net-next 01/10] mptcp: Fix up subflow's memcg when CONFIG_SOCK_CGROUP_DATA=n.
From: Shakeel Butt <shakeel.butt@linux.dev>
Date: 2025-08-14 21:44:28
Also in:
cgroups, linux-mm, mptcp
On Thu, Aug 14, 2025 at 08:08:33PM +0000, Kuniyuki Iwashima wrote:
quoted hunk ↗ jump to hunk
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 <mkoutny@suse.com> Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com> --- 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;
quoted hunk ↗ jump to hunk
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