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

[Shakeel Butt <shakeelb@google.com>]

On Fri, Feb 14, 2020 at 2:33 PM Roman Gushchin <guro@fb.com> wrote:
>
> On Fri, Feb 14, 2020 at 02:24:15PM -0800, Shakeel Butt 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.
> >
> > 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. */
>                                                                        ^^^^^
>                                                                        cgroup?
> > +     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;
> >       }
>
> Can you, please, include the stacktrace into the commit log?
> Except a minor typo (see above),
> Reviewed-by: Roman Gushchin <guro@fb.com>
>
> A really good catch.
>

Thanks, I will add the stack trace and fix the typo.

Shakeel