linux-kernel - Re: [PATCH v2] cgroup/cpuset: Extend kthread_is_per_cpu() check to all PF_NO

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Message-ID: <aB488PJUSYng6ZDQ@slm.duckdns.org>
Date: Fri, 9 May 2025 07:35:44 -1000
From: Tejun Heo <tj@...nel.org>
To: Waiman Long <longman@...hat.com>
Cc: Johannes Weiner <hannes@...xchg.org>,
	Michal Koutný <mkoutny@...e.com>,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	Xi Wang <xii@...gle.com>, Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [PATCH v2] cgroup/cpuset: Extend kthread_is_per_cpu() check to
 all PF_NO_SETAFFINITY tasks

On Thu, May 08, 2025 at 03:24:13PM -0400, Waiman Long wrote:
> Commit ec5fbdfb99d1 ("cgroup/cpuset: Enable update_tasks_cpumask()
> on top_cpuset") enabled us to pull CPUs dedicated to child partitions
> from tasks in top_cpuset by ignoring per cpu kthreads. However, there
> can be other kthreads that are not per cpu but have PF_NO_SETAFFINITY
> flag set to indicate that we shouldn't mess with their CPU affinity.
> For other kthreads, their affinity will be changed to skip CPUs dedicated
> to child partitions whether it is an isolating or a scheduling one.
> 
> As all the per cpu kthreads have PF_NO_SETAFFINITY set, the
> PF_NO_SETAFFINITY tasks are essentially a superset of per cpu kthreads.
> Fix this issue by dropping the kthread_is_per_cpu() check and checking
> the PF_NO_SETAFFINITY flag instead.
> 
> Fixes: ec5fbdfb99d1 ("cgroup/cpuset: Enable update_tasks_cpumask() on top_cpuset")
> Signed-off-by: Waiman Long <longman@...hat.com>

Applied to cgroup/for-6.15-fixes.

Thanks.

-- 
tejun