Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable
From:   Qian Cai <cai@lca.pw>
Mime-Version: 1.0 (1.0)
Subject: Re: [PATCH] mm/vmstat: Reduce zone lock hold time when reading /proc/pagetypeinfo
Date:   Thu, 24 Oct 2019 01:33:01 -0400
Message-Id: <4D23D83F-190F-40B3-9EB9-C167642321B2@lca.pw>
References: <20191023153040.c7fff4bc7c86ed605fc4667f@linux-foundation.org>
Cc:     Waiman Long <longman@redhat.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>, Roman Gushchin <guro@fb.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
        Jann Horn <jannh@google.com>, Song Liu <songliubraving@fb.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Rafael Aquini <aquini@redhat.com>
In-Reply-To: <20191023153040.c7fff4bc7c86ed605fc4667f@linux-foundation.org>
To:     Andrew Morton <akpm@linux-foundation.org>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On Oct 23, 2019, at 6:30 PM, Andrew Morton <akpm@linux-foundation.org> wro=
te:
>=20
> Yes, removing things is hard.  One approach is to add printk_once(this
> is going away, please email us if you use it) then wait a few years.=20
> Backport that one-liner into -stable kernels to hopefully speed up the
> process.

Although it still look like an overkill to me given,

1) Mel given a green light to remove it.
2) Nobody justifies any sensible reason to keep it apart from it was probabl=
y only triggering by some testing tools blindly read procfs entries.

it is still better than wasting developers=E2=80=99 time to beating the =E2=80=
=9Cdead=E2=80=9D horse.

>=20
> Meanwhile, we need to fix the DoS opportunity.  How about my suggestion
> that we limit the count to 1024, see if anyone notices?  I bet they
> don't!

The DoS is probably there since the file had been introduced  almost 10 year=
s ago, so I suspect it is not that easily exploitable.=