From: Glauber Costa Date: Tue, 31 Jul 2012 23:43:07 +0000 (-0700) Subject: memcg: fix bad behavior in use_hierarchy file X-Git-Tag: v3.6-rc1~24^2~74 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=567fb435bb7a37afda35902b884562c40756dc45;p=platform%2Fkernel%2Flinux-3.10.git memcg: fix bad behavior in use_hierarchy file 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. So test 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 Acked-by: Michal Hocko Cc: Kamezawa Hiroyuki Acked-by: Johannes Weiner Cc: Ying Han Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 55a85e1..6d3dd54 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3764,6 +3764,10 @@ 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 @@ -3780,6 +3784,8 @@ static int mem_cgroup_hierarchy_write(struct cgroup *cont, struct cftype *cft, retval = -EBUSY; } else retval = -EINVAL; + +out: cgroup_unlock(); return retval;