From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx151.postini.com [74.125.245.151]) by kanga.kvack.org (Postfix) with SMTP id 07E436B0071 for ; Tue, 26 Jun 2012 11:50:05 -0400 (EDT) From: Glauber Costa Subject: [PATCH 1/2] fix bad behavior in use_hierarchy file Date: Tue, 26 Jun 2012 19:47:13 +0400 Message-Id: <1340725634-9017-2-git-send-email-glommer@parallels.com> In-Reply-To: <1340725634-9017-1-git-send-email-glommer@parallels.com> References: <1340725634-9017-1-git-send-email-glommer@parallels.com> Sender: owner-linux-mm@kvack.org List-ID: To: cgroups@vger.kernel.org Cc: linux-mm@kvack.org, kamezawa.hiroyu@jp.fujitsu.com, Michal Hocko , Johannes Weiner , Andrew Morton , Glauber Costa , Dhaval Giani 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 --- 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, 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