On Thu, Aug 11, 2016 at 04:45:11PM +0200, Peter Zijlstra wrote: > On Thu, Aug 04, 2016 at 05:51:20PM +0800, Wanpeng Li wrote: > > From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> > > > > The dl task will be replenished after dl task timer fire and start a new > > period. It will be enqueued and to re-evaluate its dependency on the tick > > in order to restart it. However, if cpu is hot-unplug, irq_work_queue will > > splash since the target cpu is offline. > > > > As a result: > > > > WARNING: CPU: 2 PID: 0 at kernel/irq_work.c:69 irq_work_queue_on+0xad/0xe0 > > Call Trace: > > dump_stack+0x99/0xd0 > > __warn+0xd1/0xf0 > > warn_slowpath_null+0x1d/0x20 > > irq_work_queue_on+0xad/0xe0 > > tick_nohz_full_kick_cpu+0x44/0x50 > > tick_nohz_dep_set_cpu+0x74/0xb0 > > enqueue_task_dl+0x226/0x480 > > activate_task+0x5c/0xa0 > > dl_task_timer+0x19b/0x2c0 > > ? push_dl_task.part.31+0x190/0x190 > > Hurm, so this is after hot-unplug succeeded. We get a timer (which is > also already migrated), but we enqueue the dl task on the offline CPU, > because we need to do replenish because start_dl_timer() -- see the > comment in dl_task_timer() at #ifdef CONFIG_SMP. > > Then, once we've enqueued the task on the offline cpu, do we migrate it. > > Bit icky that, but I don't immediately see a better way. > > And I think you're right in that we don't leak the nohz state, the > migration, which we do immediately after this, takes care of that. Are you sure there is no way the hotplug can fail after this stage? I see this is at the end of the CPUHP_AP callbacks. Nothing else can fail afterward? If so then yes we are ok as migration takes care of the tick dependency. Thanks. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
