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://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=567fb435bb7a37afda35902b884562c40756dc45;p=pandora-kernel.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 --- Reading git-diff-tree failed