From: Michal Hocko Date: Fri, 26 Oct 2012 11:37:29 +0000 (+0200) Subject: memcg: root_cgroup cannot reach mem_cgroup_move_parent X-Git-Tag: master-2012-12-14~17^2~47^2~9 X-Git-Url: http://pileus.org/git/?a=commitdiff_plain;h=d842301181d9a4486aa24720ed4f96018b213292;p=~andy%2Flinux memcg: root_cgroup cannot reach mem_cgroup_move_parent The root cgroup cannot be destroyed so we never hit it down the mem_cgroup_pre_destroy path and mem_cgroup_force_empty_write shouldn't even try to do anything if called for the root. This means that mem_cgroup_move_parent doesn't have to bother with the root cgroup and it can assume it can always move charges upwards. Signed-off-by: Michal Hocko Reviewed-by: Tejun Heo Reviewed-by: Glauber Costa Signed-off-by: Tejun Heo --- diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 07d92b84f44..916132a29b3 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2715,9 +2715,7 @@ static int mem_cgroup_move_parent(struct page *page, unsigned long uninitialized_var(flags); int ret; - /* Is ROOT ? */ - if (mem_cgroup_is_root(child)) - return -EINVAL; + VM_BUG_ON(mem_cgroup_is_root(child)); ret = -EBUSY; if (!get_page_unless_zero(page)) @@ -3823,6 +3821,8 @@ static int mem_cgroup_force_empty_write(struct cgroup *cont, unsigned int event) struct mem_cgroup *memcg = mem_cgroup_from_cont(cont); int ret; + if (mem_cgroup_is_root(memcg)) + return -EINVAL; css_get(&memcg->css); ret = mem_cgroup_force_empty(memcg); css_put(&memcg->css);