On Tue, Feb 07, 2017 at 01:37:08PM +0100, Michal Hocko wrote: > > You cannot put sleepable lock inside the preempt disbaled section... > > We can make it a spinlock right? > > Scratch that! For some reason I thought that cpu notifiers are run in an > atomic context. Now that I am checking the code again it turns out I was > wrong. __cpu_notify uses __raw_notifier_call_chain so this is not an > atomic context. Indeed. > Anyway, shouldn't be it sufficient to disable preemption > on drain_local_pages_wq? That would be sufficient for a hot-removed CPU moving the drain request to another CPU and avoiding any scheduling events. > The CPU hotplug callback will not preempt us > and so we cannot work on the same cpus, right? > I don't see a specific guarantee that it cannot be preempted and it would depend on an the exact cpu hotplug implementation which is subject to quite a lot of change. Hence, the mutex provides a guantee that the hot-removed CPU teardown cannot run on the same CPU as a workqueue drain running on a CPU it was not originally scheduled for. -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
