On Fri 12-07-13 11:48:36, Tejun Heo wrote: > On Fri, Jul 12, 2013 at 11:24:56AM +0200, Michal Hocko wrote: > > Cgroup events are unregistered from the workqueue context by > > cgroup_event_remove scheduled by cgroup_destroy_locked (when a cgroup is > > removed by rmdir). > > > > cgroup_event_remove removes the eventfd wait queue from the work > > queue, then it unregisters all the registered events and finally > > puts a reference to the cgroup dentry. css_free which triggers memcg > > deallocation is called after the last reference is dropped. > > > > The scheduled vmpressure work item either happens before > > cgroup_event_remove or it is not triggered at all so it always happen > > _before_ the last dput thus css_free. > > I don't follow what the above has to do with ensuring work item > execution is finished before the underlying data structure is > released. How are the above relevant? What am I missing here? OK, it seems I managed to confuse myself. I thought that remove_wait_queue(event->wqh, &event->wait) called from cgroup_event_remove guarantee that vmpr event would go away with that workqueue. But now that I am looking at it, vmpr->work seems to be living in a completely independent queue. > > This patch just documents this trickiness. > > This doesn't have to be tricky at all. It's a *completely* routine > thing. Would you please stop making it one? Fair enough. I will repost the series shortly. -- Michal Hocko 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>