Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> writes: >>>>> >>>>> We test RES_USAGE before taking hugetlb_lock. What prevents some other >>>>> thread from increasing RES_USAGE after that test? >>>>> >>>>> After walking the list we test RES_USAGE after dropping hugetlb_lock. >>>>> What prevents another thread from incrementing RES_USAGE before that >>>>> test, triggering the BUG? >>>> >>>> IIUC core cgroup will prevent a new task getting added to the cgroup >>>> when we are in pre_destroy. Since we already check that the cgroup doesn't >>>> have any task, the RES_USAGE cannot increase in pre_destroy. >>>> >>> >>> >>> You're wrong here. We release cgroup_lock before calling pre_destroy and retrieve >>> the lock after that, so a task can be attached to the cgroup in this interval. >>> >> >> But that means rmdir can be racy right ? What happens if the task got >> added, allocated few pages and then moved out ? We still would have task >> count 0 but few pages, which we missed to to move to parent cgroup. >> > > That's a problem even if it's verrrry unlikely. > I'd like to look into it and fix the race in cgroup layer. > But I'm sorry I'm a bit busy in these days... > How about moving that mutex_unlock(&cgroup_mutex) to memcg callback ? That can be a patch for 3.5 ? -aneesh -- 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>