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mptcp: Fix up subflow's memcg when CONFIG_SOCK_CGROUP_DATA=n.

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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: 3764b0c565 ("mptcp: attach subflow socket to parent cgroup")
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Acked-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Link: https://patch.msgid.link/20250815201712.1745332-2-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Kuniyuki Iwashima
2025-08-15 20:16:09 +00:00
committed by Jakub Kicinski
parent 5c69e0b395
commit 68889dfd54
3 changed files with 22 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/memcontrol.h
View File

@@ -1604,6 +1604,7 @@ extern struct static_key_false memcg_sockets_enabled_key;
#define mem_cgroup_sockets_enabled static_branch_unlikely(&memcg_sockets_enabled_key)
void mem_cgroup_sk_alloc(struct sock *sk);
void mem_cgroup_sk_free(struct sock *sk);
void mem_cgroup_sk_inherit(const struct sock *sk, struct sock *newsk);
#if BITS_PER_LONG < 64
static inline void mem_cgroup_set_socket_pressure(struct mem_cgroup *memcg)
@@ -1661,6 +1662,11 @@ void reparent_shrinker_deferred(struct mem_cgroup *memcg);
#define mem_cgroup_sockets_enabled 0
static inline void mem_cgroup_sk_alloc(struct sock *sk) { };
static inline void mem_cgroup_sk_free(struct sock *sk) { };
static inline void mem_cgroup_sk_inherit(const struct sock *sk, struct sock *newsk)
{
}
static inline bool mem_cgroup_under_socket_pressure(struct mem_cgroup *memcg)
{
return false;

13
mm/memcontrol.c
View File

@@ -5024,6 +5024,19 @@ void mem_cgroup_sk_free(struct sock *sk)
css_put(&sk->sk_memcg->css);
}
void mem_cgroup_sk_inherit(const struct sock *sk, struct sock *newsk)
{
if (sk->sk_memcg == newsk->sk_memcg)
return;
mem_cgroup_sk_free(newsk);
if (sk->sk_memcg)
css_get(&sk->sk_memcg->css);
newsk->sk_memcg = sk->sk_memcg;
}
/**
* mem_cgroup_charge_skmem - charge socket memory
* @memcg: memcg to charge

11
net/mptcp/subflow.c
View File

@@ -1717,19 +1717,14 @@ 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);
}
#endif /* CONFIG_SOCK_CGROUP_DATA */
if (mem_cgroup_sockets_enabled)
mem_cgroup_sk_inherit(parent, child);
}
static void mptcp_subflow_ops_override(struct sock *ssk)