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From:   Shakeel Butt <shakeelb@google.com>
Date:   Wed, 26 Feb 2020 12:02:31 -0800
Message-ID: <CALvZod5TsauERhaCqa1OZp4FaX4nq_UBL84=siESEG=Uk4LYuQ@mail.gmail.com>
Subject: Re: [PATCH v3] cgroup: memcg: net: do not associate sock with
 unrelated cgroup
To:     David Miller <davem@davemloft.net>
Cc:     Eric Dumazet <edumazet@google.com>, Roman Gushchin <guro@fb.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Tejun Heo <tj@kernel.org>, Greg Thelen <gthelen@google.com>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Cgroups <cgroups@vger.kernel.org>, Linux MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>
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On Wed, Feb 26, 2020 at 11:07 AM David Miller <davem@davemloft.net> wrote:
>
> From: Shakeel Butt <shakeelb@google.com>
> Date: Thu, 20 Feb 2020 17:46:04 -0800
>
> > 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.
> >
> > WARNING: Please note that about half of the TCP sockets are allocated
> > from the IRQ context, so, memory used by such sockets will not be
> > accouted by the memcg.
>
> Then if we do this then we have to have some kind of subsequent change
> to attach these sockets to the correct cgroup, right?

Currently we can potentially charge wrong cgroup. With this patch that
will be fixed but potentially half of sockets remain unaccounted. I
have a followup (incomplete) patch [1] to fix that. I will send the
next version soon.

[1] https://lore.kernel.org/linux-mm/20200222010456.40635-1-shakeelb@google.com/