>> especially while shutting down objects as they enter a lingering stage >> where they're de-registered but not destroyed and you should be >> careful which parts of the object are still accessible. I haven't >> read it carefully but here I'm not sure whether it's safe to do event >> related operations after removal. From cgroup core side, event list >> is shut down synchronously from cgroup_destroy_locked(). It doesn't >> seem like that part is explicitly built to remain accessible >> afterwards. > > /me goes and checks the code > > vmpressure_event sends signals to _registered_ events but those are > unregistered from the work queue context by cgroup_event_remove (via > vmpressure_unregister_event) queued from cgroup_destroy_locked. > > I am not sure what are the guarantees for ordering on the workqueue but > this all suggests that either vmpressure_event sees an empty vmpr->events > or it can safely send signals as cgroup_event_remove is pending on the > queue. > > cgroup_event_remove drops a reference to cgrp->dentry after everything > is unregistered and event->wait removed from the wait queue so > cgroup_free_fn couldn't have been called yet and so memcg is still > alive. This means that even css_get/put is not necessary. > > So I guess we are safe with the code as is but this all is really > _tricky_ and deserves a fat comment. So rather than adding flushing work > item code we should document it properly. > > Or am I missing something? > But if I read the code correctly, even no one registers a vmpressure event, vmpressure() is always running and queue the work item. -- 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>