linux-kernel - Re: [PATCH v4 2/6] cgroup/cpuset: Properly handle partition root tree

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Date:   Wed, 11 Aug 2021 08:08:41 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Shuah Khan <shuah@...nel.org>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>, Phil Auld <pauld@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Michal Koutný <mkoutny@...e.com>
Subject: Re: [PATCH v4 2/6] cgroup/cpuset: Properly handle partition root tree

Hello,

On Tue, Aug 10, 2021 at 11:06:03PM -0400, Waiman Long wrote:
> For a partition root tree with parent and child partition roots, this
> patch will now prohibit changing parent partition root back to member
> as changes to "cpuset.cpus.partition" should not cause those child
> partition roots to become invalid.

So, the general rule is that a descendant should never be able to affect or
restrict what an ancestor can do in terms of configuration. This is because
descendant cgroups can be delegated and a system manager sitting at a higher
level in the hierarchy may not have much control over what happens under
delegated subtrees.

Given that we're promoting the error state as the first class citizen in the
interface anyway, wouldn't it be better to keep this in line too?

Thanks.

-- 
tejun