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From:   Eric Dumazet <edumazet@google.com>
Date:   Fri, 14 Feb 2020 16:11:24 -0800
Message-ID: <CANn89iKq5r7aCDdpTXzfvDbhHYgnTGhgyTG5_rLbcSeeF8uJJQ@mail.gmail.com>
Subject: Re: [PATCH v2] cgroup: memcg: net: do not associate sock with
 unrelated cgroup
To:     Shakeel Butt <shakeelb@google.com>
Cc:     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>,
        Roman Gushchin <guro@fb.com>,
        LKML <linux-kernel@vger.kernel.org>
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On Fri, Feb 14, 2020 at 4:04 PM Shakeel Butt <shakeelb@google.com> wrote:
>
> On Fri, Feb 14, 2020 at 3:12 PM Eric Dumazet <edumazet@google.com> wrote:
> >
> > On Fri, Feb 14, 2020 at 2:48 PM Shakeel Butt <shakeelb@google.com> wrote:
> >
> > >
> > > I think in the current code if the association is skipped at
> > > allocation time then the sock will remain unassociated for its
> > > lifetime.
> > >
> > > Maybe we can add the association in the later stages but it seems like
> > > it is not a simple task i.e. edbe69ef2c90f ("Revert "defer call to
> > > mem_cgroup_sk_alloc()"").
> >
> > Half TCP sockets are passive, so this means that 50% of TCP sockets
> > won't be charged.
> > (the socket cloning always happens from BH context)
> >
> > I think this deserves a comment in the changelog or documentation,
> > otherwise some people might think
> > using memcg will make them safe.
>
> Thanks I will update the changelog. Also is inet_csk_accept() the
> right place for delayed cgroup/memcg binding (if we decide to do
> that). I am wondering if we can force charge the memcg during late
> binding to cater the issue fixed in edbe69ef2c90f.
>

Yes, this is exactly why accept() would be the natural choice.

You  do not want to test/change the binding at sendmsg()/recvmsg() time, right ?