On Mon, Oct 10, 2016 at 04:34:48PM +0800, Wanpeng Li wrote: > > If there is a need to kick the idle load balancer, an ILB will be selected > > to perform nohz idle load balance, however, if the selected ILB is in the > > process of offline, smp_sched_reschedule() which generates a sched IPI will > > splat as above. > > > > CPU0 CPU1 > > > > find_new_ilb() > > set_rq_offline() > > smp_sched_reschedule() Oops > > nohz_balance_exit_idle() > > > > This patch fix it by exiting nohz idle balance before set cpu offline. > > CPU 0 CPU1 > > find_new_ilb() > nohz_balance_exit_idle() > set_rq_offline() > smp_sched_reschedule() > > It seems that the patch still can't avoid this race, so any proposal > is a great appreciated. :)
Not sure how this can happen, scheduler_tick() -> trigger_load_balance() -> nohz_balancer_kick() is called with IRQs disabled, this too implies a RCU-sched read side section. And hotplug explicitly includes a rcu_sync_sched(). It would be find_new_ilb() is 'broken' in that it considers !active CPUs. That's not immediately obvious.
