memcg: do not expose uninitialized mem_cgroup_per_node to world

If somebody is touching data too early, it might be easier to diagnose a
problem when dereferencing NULL at mem->info.nodeinfo[node] than trying to
understand why mem_cgroup_per_zone is [un|partly]initialized.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c02d870..f6c4beb 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4742,7 +4742,6 @@ static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *memcg, int node)
        if (!pn)
                return 1;
 
-       memcg->info.nodeinfo[node] = pn;
        for (zone = 0; zone < MAX_NR_ZONES; zone++) {
                mz = &pn->zoneinfo[zone];
                for_each_lru(l)
@@ -4751,6 +4750,7 @@ static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *memcg, int node)
                mz->on_tree = false;
                mz->mem = memcg;
        }
+       memcg->info.nodeinfo[node] = pn;
        return 0;
 }