linux-kernel - Re: [RFC PATCH] cpuset: Allow setscheduler regardless of manipulated task

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Message-ID: <20220624124316.GH16004@blackbody.suse.cz>
Date:   Fri, 24 Jun 2022 14:43:16 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Waiman Long <longman@...hat.com>
Cc:     cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>
Subject: Re: [RFC PATCH] cpuset: Allow setscheduler regardless of manipulated
 task

On Thu, Jun 23, 2022 at 02:44:33PM -0400, Waiman Long <longman@...hat.com> wrote:
> That could be an issue.

The way how I understand here is that the privileged process isn't part
of contrained workload (if it were then, it can modify cpuset itself)
like debugging or tracing a code within a container entered by the
admin. The bypass could not be used to setscheduler (via migration) of
an arbitrary process.

> What do you mean by nothing effectively changes?

It's a freshly created child (after cpuset_css_online()), so it inherits
parent's attributes, so the migration from the parent to this child
doesn't affect CPU affinity etc.

> Since the check is done on a taskset level, if only one of the tasks in the
> taskset fails, the whole taskset fails. Maybe we should consider an option
> for task based migration. So all the tasks that can be migrated will be
> migrated and the rests will be left behind in the original cpuset.

Hm, I haven't thought about that. That might be in theory possible for
threaded controllers (like cpuset) but I imagine it'd a bit messy, in
particular for these implicit migrations upon controller enablement.

Thanks,
Michal

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