Kamezawa Hiroyuki <kamezawa.hir...@jp.fujitsu.com> 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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
