linux-kernel - Re: [PATCH 4/4] cgroup: Do not report unavailable v1 controllers in /proc/cgroups

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Message-ID: <bio4h3soa5a64zqca66fbtmur3bzwhggobplzg535erpfr2qxe@xsgzgxihirpa>
Date: Fri, 11 Jul 2025 15:10:44 +0200
From: Michal Koutný <mkoutny@...e.com>
To: Ben Hutchings <ben@...adent.org.uk>
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>, 
	Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Shakeel Butt <shakeel.butt@...ux.dev>, 
	Muchun Song <muchun.song@...ux.dev>, Andrew Morton <akpm@...ux-foundation.org>, 
	Chen Ridong <chenridong@...wei.com>, 1108294@...s.debian.org
Subject: Re: [PATCH 4/4] cgroup: Do not report unavailable v1 controllers in
 /proc/cgroups

Hello Ben.

On Wed, Jul 09, 2025 at 08:22:09PM +0200, Ben Hutchings <ben@...adent.org.uk> wrote:
> Would you consider reverting this change for the sake of compatibility?

As you write, it's not fatally broken and it may be "just" an issue of
container images that got no fresh rebuild. (And I think it should be
generally discouraged running containers with stale deps in them.)

The original patch would mainly serve legacy userspace (host) setups on
top of contemporary kernel (besides API purity reasons). Admittedly,
these should be rare and eventually extinct in contrast with your
example where it's a containerized userspace (which typically could do
no cgroup setup) that may still have some user demand.

So, I'd be more confident with the revert if such an adjustment was
carried downstream by some distro and proven its viability first. Do you
know of any in the wild?

I appreciate your report,
Michal