linux-kernel - Re: [PATCH 4/9] cgroup: Print warning when /proc/cgroups is read on v2-only system

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Message-ID: <9c24f14f-c7a8-490e-9077-0d977d175d89@redhat.com>
Date: Wed, 5 Mar 2025 11:27:33 -0500
From: Waiman Long <llong@...hat.com>
To: Michal Koutný <mkoutny@...e.com>,
 Tejun Heo <tj@...nel.org>
Cc: cgroups@...r.kernel.org, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, Josef Bacik <josef@...icpanda.com>,
 Jens Axboe <axboe@...nel.dk>, Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH 4/9] cgroup: Print warning when /proc/cgroups is read on
 v2-only system


On 3/5/25 5:17 AM, Michal Koutný wrote:
> On Tue, Mar 04, 2025 at 06:55:02AM -1000, Tejun Heo <tj@...nel.org> wrote:
>> I'm hoping that we could deprecate /proc/cgroups entirely. Maybe we can just
>> warn whenever the file is accessed?
> I added the guard with legacy systems (i.e. make this backportable) in
> mind which start with no cgroupfs mounted at all and until they decide
> to continue either v1 or v2 way, looking at /proc/cgroups is fine.
> It should warn users that look at /proc/cgroups in cases when it bears
> no valid information.

I like the idea of warning users about using /etc/cgroups if no v1 
filesystem is mounted. It makes sense to make it backportable to older 
kernel. We can always add a follow-up patch later to always warn about it.

Acked-by: Waiman Long <longman@...hat.com>