linux-kernel - Re: [PATCH 1/2] cpuset: Fix cpuset_cpus_allowed() to not filter offline CPUs

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Date:   Fri, 3 Feb 2023 16:26:23 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        kernel-team@...roid.com, Zefan Li <lizefan.x@...edance.com>,
        Tejun Heo <tj@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org
Subject: Re: [PATCH 1/2] cpuset: Fix cpuset_cpus_allowed() to not filter
 offline CPUs

On Fri, Feb 03, 2023 at 10:13:10AM -0500, Waiman Long wrote:

> I think I know where the problem is. It is due to the fact the cpuset
> hotplug code doesn't update cpumasks of the tasks in the top cpuset (root)
> at all when there is a cpu offline or online event. It is probably because
> for some of the tasks in the top cpuset, especially the percpu kthread,
> changing their cpumasks can be catastrophic. The hotplug code does update
> the cpumasks of the tasks that are not in the top cpuset. This problem is
> irrespective of whether v1 or v2 is in use.

I've been saying this exact thing for how many mails now?