linux-kernel - Re: [PATCH v11 7/8] cgroup/cpuset: Update description of cpuset.cpus.partition in cgroup-v2.rst

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Date:   Mon, 13 Jun 2022 19:55:49 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Waiman Long <longman@...hat.com>,
        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>
Subject: Re: [PATCH v11 7/8] cgroup/cpuset: Update description of
 cpuset.cpus.partition in cgroup-v2.rst

On Mon, Jun 13, 2022 at 07:28:25AM -1000, Tejun Heo <tj@...nel.org> wrote:
> I see. Is this part even necessary? All the .cpus files of the siblings are
> owned by the parent who's responsible for configuring both the mode that the
> cgroup subtree is gonna be in and their cpumasks. 

Do you mean such an example:

    parent	cpuset.cpus=SET (root)	cpuset.cpus.partition=isolated 
    `- child_1	cpuset.cpus=partition_of(SET) (root)	cpuset.cpus.partition=isolated
    `- ...
    `- child_n	cpuset.cpus=partition_of(SET) (root)	cpuset.cpus.partition=isolated
?

I don't think child_*/cpuset.cpus must be owned by root.
Actually, the root would only configure the parent, i.e.
parent/cpuset.cpus (whose changes would be disallowed to the
unprivileged tasks) and the distribution among siblings would up to the
whatever runs below.

> Given that all the other errors it can make are notified through
> "invalid (REASON)" in the mode file, wouldn't it fit better to notify
> cpus configuration error the same way too?

Do you suggest that a write into child_*/cpuset.cpus that'd not be
exclusive wrt a sibling would result in an error string in
parent/cpuset.cpus.partition?

Thanks,
Michal

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