linux-kernel - Re: [PATCH/for-next v4 2/4] cgroup/cpuset: Defer housekeeping_update() calls from CPU hotplug to workqueue

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Message-ID: <aYZrJaIIbTX4E-nO@pavilion.home>
Date: Fri, 6 Feb 2026 23:28:53 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Waiman Long <longman@...hat.com>
Cc: Chen Ridong <chenridong@...weicloud.com>, Tejun Heo <tj@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Koutný <mkoutny@...e.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Thomas Gleixner <tglx@...utronix.de>, Shuah Khan <shuah@...nel.org>,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH/for-next v4 2/4] cgroup/cpuset: Defer
 housekeeping_update() calls from CPU hotplug to workqueue

Le Fri, Feb 06, 2026 at 03:37:10PM -0500, Waiman Long a écrit :
> The update_isolation_cpumasks() function can be called either directly
> from regular cpuset control file write with cpuset_full_lock() called
> or via the CPU hotplug path with cpus_write_lock and cpuset_mutex held.
> 
> As we are going to enable dynamic update to the nozh_full housekeeping
> cpumask (HK_TYPE_KERNEL_NOISE) soon with the help of CPU hotplug,
> allowing the CPU hotplug path to call into housekeeping_update() directly
> from update_isolation_cpumasks() will likely cause deadlock. So we

Why do we need to call housekeeping_update() from hotplug? I would
expect it to be called only when cpuset control file are written since
housekeeping cpumask don't deal with online CPUs but with possible
CPUs.

Thanks.

-- 
Frederic Weisbecker
SUSE Labs