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The cpuset_handle_hotplug() may need to invoke housekeeping_update(), for instance, when an isolated partition is invalidated because its last active CPU has been put offline. 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 have to defer any call to housekeeping_update() after the CPU hotplug operation has finished. This is now done via the workqueue where the update_hk_sched_domains() function will be invoked via the hk_sd_workfn(). An concurrent cpuset control file write may have executed the required update_hk_sched_domains() function before the work function is called. So the work function call may become a no-op when it is invoked. Signed-off-by: Waiman Long <longman@redhat.com> Signed-off-by: Tejun Heo <tj@kernel.org>