On Thu 19-07-12 16:56:18, Aneesh Kumar K.V wrote: > 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 ? Bahh, I have just posted a follow up on mm-commits email exactly about this. Sorry I have missed that the discussion is still ongoing. I have posted also something I guess should help. Can we follow up on that one or should I post the patch here as well? > > -aneesh > > -- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic -- 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>