Re: [PATCH v3 net-next 01/12] mptcp: Fix up subflow's memcg when CONFIG_SOCK_CGROUP_DATA=n.
From: Matthieu Baerts <matttbe@kernel.org>
Date: 2025-08-13 08:54:33
Also in:
cgroups, linux-mm, mptcp
Hi Kuniyuki, On 12/08/2025 19:58, 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().
Thank you for the patch! Acked-by: Matthieu Baerts (NGI0) <matttbe@kernel.org> Cheers, Matt -- Sponsored by the NGI0 Core fund.