linux-kernel - Re: [PATCH v2] cpuset: handle race between CPU hotplug and cpuset_hotplug

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Message-ID: <20160913152738.GB21123@htj.duckdns.org>
Date:   Tue, 13 Sep 2016 11:27:38 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Joonwoo Park <joonwoop@...eaurora.org>
Cc:     Li Zefan <lizefan@...wei.com>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2] cpuset: handle race between CPU hotplug and
 cpuset_hotplug_work

On Sun, Sep 11, 2016 at 09:14:58PM -0700, Joonwoo Park wrote:
> A discrepancy between cpu_online_mask and cpuset's effective_cpus
> mask is inevitable during hotplug since cpuset defers updating of
> effective_cpus mask using a workqueue, during which time nothing
> prevents the system from more hotplug operations.  For that reason
> guarantee_online_cpus() walks up the cpuset hierarchy until it finds
> an intersection under the assumption that top cpuset's effective_cpus
> mask intersects with cpu_online_mask even with such a race occurring.
> 
> However a sequence of CPU hotplugs can open a time window, during which
> none of the effective CPUs in the top cpuset intersect with
> cpu_online_mask.

Applied to cgroup/for-4.8-fixes.

Thanks.

-- 
tejun