----->
CPU that offilines                             CPU offlining
-----------------                             ---------------------
cpu_down() {
    __stop_machine(take_cpu_down)

                                               take_cpu_down() {
                                                   __cpu_disable() {
                                                      * disable irqs in hw
                                                      * clear from online mask
                                                   }
                                                   move all tasks somewhere
                                               }
while (!idle_cpu(offlining))
    cpu_relax()

cpu_die();
<---------