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authorGlauber Costa <glommer@parallels.com>2012-07-31 16:43:07 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-07-31 18:42:43 -0700
commit567fb435bb7a37afda35902b884562c40756dc45 (patch)
tree71c4cec3ab02bd69eafbfd98d38774466d52843e
parentca28ddc908fcfef0e5c1b6e5df632db7fc26de10 (diff)
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 <glommer@parallels.com> Cc: Dhaval Giani <dhaval.giani@gmail.com> Acked-by: Michal Hocko <mhocko@suse.cz> Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Cc: Ying Han <yinghan@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/memcontrol.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 55a85e1a342f..6d3dd54ec429 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;