From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx206.postini.com [74.125.245.206]) by kanga.kvack.org (Postfix) with SMTP id B069A6B005C for ; Tue, 26 Jun 2012 11:52:32 -0400 (EDT) Date: Tue, 26 Jun 2012 17:52:29 +0200 From: Michal Hocko Subject: Re: [PATCH 1/2] fix bad behavior in use_hierarchy file Message-ID: <20120626155229.GH9566@tiehlicka.suse.cz> References: <1340725634-9017-1-git-send-email-glommer@parallels.com> <1340725634-9017-2-git-send-email-glommer@parallels.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1340725634-9017-2-git-send-email-glommer@parallels.com> Sender: owner-linux-mm@kvack.org List-ID: To: Glauber Costa Cc: cgroups@vger.kernel.org, linux-mm@kvack.org, kamezawa.hiroyu@jp.fujitsu.com, Johannes Weiner , Andrew Morton , Dhaval Giani On Tue 26-06-12 19:47:13, Glauber Costa wrote: > I have an application that does the following: > > * copy the state of all controllers attached to a hierarchy > * replicate it as a child of the current level. > > I would expect writes to the files to mostly succeed, since they > are inheriting sane values from parents. > > But that is not the case for use_hierarchy. If it is set to 0, we > succeed ok. If we're set to 1, the value of the file is automatically > set to 1 in the children, but if userspace tries to write the > very same 1, it will fail. That same situation happens if we > set use_hierarchy, create a child, and then try to write 1 again. > > Now, there is no reason whatsoever for failing to write a value > that is already there. It doesn't even match the comments, that > states: > > /* If parent's use_hierarchy is set, we can't make any modifications > * in the child subtrees... > > since we are not changing anything. > > The following patch tests the new value against the one we're storing, > and automatically return 0 if we're not proposing a change. > > Signed-off-by: Glauber Costa > CC: Dhaval Giani > CC: Michal Hocko > CC: Kamezawa Hiroyuki > CC: Johannes Weiner Acked-by: Michal Hocko > --- > mm/memcontrol.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index df8c9fb..85f7790 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -3989,6 +3989,10 @@ static int mem_cgroup_hierarchy_write(struct cgroup *cont, struct cftype *cft, > parent_memcg = mem_cgroup_from_cont(parent); > > cgroup_lock(); > + > + if (memcg->use_hierarchy == val) > + goto out; > + > /* > * If parent's use_hierarchy is set, we can't make any modifications > * in the child subtrees. If it is unset, then the change can > @@ -4005,6 +4009,8 @@ static int mem_cgroup_hierarchy_write(struct cgroup *cont, struct cftype *cft, > retval = -EBUSY; > } else > retval = -EINVAL; > + > +out: > cgroup_unlock(); > > return retval; > -- > 1.7.10.2 > > -- > To unsubscribe from this list: send the line "unsubscribe cgroups" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- 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@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org