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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aYtSyCb1EioSuDep@localhost.localdomain>
Date: Tue, 10 Feb 2026 16:46:16 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Waiman Long <llong@...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 Sat, Feb 07, 2026 at 09:00:45PM -0500, Waiman Long a écrit :
> On 2/6/26 5:28 PM, Frederic Weisbecker wrote:
> > 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.
> 
> It needs to call housekeeping_update() only in the special case where there
> is only one active CPU in an isolated partition and that CPU goes offline.
> In this case, the partition becomes disabled that causes change in the
> isolated CPUs. I know this special case shouldn't happen in real world, but
> I do have test case to test that.

But why is that needed? This isn't changing the mask of domain isolated CPUs.
Only their onlineness. I mean timers, workqueue, kthreads all have their
hotplug callbacks able to deal with that already.

> Theoretically, we can add code to handle this special case to keep this
> offline isolated CPU in a special pool without changing isolated_cpus and
> hence  HK_TYPE_DOMAIN cpumask. In this way, we shouldn't need to call
> housekeeping_update() from CPU hotplug. I will probably do that as CPU
> hotplug will be used when we make HK_TYPE_KERNEL_NOISE cpumask dynamic in
> the near future.

That doesn't look necessary.

Thanks.

-- 
Frederic Weisbecker
SUSE Labs