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From:   Eric Dumazet <edumazet@google.com>
Date:   Fri, 14 Feb 2020 15:12:28 -0800
Message-ID: <CANn89i+-GJgD4-YnF9yKhDvG48OK8XtM7oB9gw6njeb_ZbdpDw@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 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.