Re: [PATCH v2] cgroup: memcg: net: do not associate sock with unrelated cgroup

[Eric Dumazet <edumazet@google.com>]

On Fri, Feb 14, 2020 at 2:24 PM Shakeel Butt <shakeelb@google.com> wrote:
>
> We are testing network memory accounting in our setup and noticed
> inconsistent network memory usage and often unrelated cgroups network
> usage correlates with testing workload. On further inspection, it
> seems like mem_cgroup_sk_alloc() and cgroup_sk_alloc() are broken in
> irq context specially for cgroup v1.
>
> mem_cgroup_sk_alloc() and cgroup_sk_alloc() can be called in irq context
> and kind of assumes that this can only happen from sk_clone_lock()
> and the source sock object has already associated cgroup. However in
> cgroup v1, where network memory accounting is opt-in, the source sock
> can be unassociated with any cgroup and the new cloned sock can get
> associated with unrelated interrupted cgroup.
>
> Cgroup v2 can also suffer if the source sock object was created by
> process in the root cgroup or if sk_alloc() is called in irq context.
> The fix is to just do nothing in interrupt.

So, when will the association be done ?
At accept() time ?
Is it done already ?

Thanks


>
> Fixes: 2d7580738345 ("mm: memcontrol: consolidate cgroup socket tracking")
> Fixes: d979a39d7242 ("cgroup: duplicate cgroup reference when cloning sockets")
> Signed-off-by: Shakeel Butt <shakeelb@google.com>
> ---
>
> Changes since v1:
> - Fix cgroup_sk_alloc() too.
>
>  kernel/cgroup/cgroup.c | 4 ++++
>  mm/memcontrol.c        | 4 ++++
>  2 files changed, 8 insertions(+)
>
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index 9a8a5ded3c48..46e5f5518fba 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -6449,6 +6449,10 @@ void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
>                 return;
>         }
>
> +       /* Do not associate the sock with unrelated interrupted task's memcg. */
> +       if (in_interrupt())
> +               return;
> +
>         rcu_read_lock();
>
>         while (true) {
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 63bb6a2aab81..f500da82bfe8 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -6697,6 +6697,10 @@ void mem_cgroup_sk_alloc(struct sock *sk)
>                 return;
>         }
>
> +       /* Do not associate the sock with unrelated interrupted task's memcg. */
> +       if (in_interrupt())
> +               return;
> +
>         rcu_read_lock();
>         memcg = mem_cgroup_from_task(current);
>         if (memcg == root_mem_cgroup)
> --
> 2.25.0.265.gbab2e86ba0-goog
>