From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: mm/memcg: iteration skip memcgs not yet fully initialized
It is surprising that the mem_cgroup iterator can return memcgs which have
not yet been fully initialized. By accident (or trial and error?) this
appears not to present an actual problem; but it may be better to prevent
such surprises, by skipping memcgs not yet online.
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [3.12+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff -puN mm/memcontrol.c~mm-memcg-iteration-skip-memcgs-not-yet-fully-initialized mm/memcontrol.c
--- a/mm/memcontrol.c~mm-memcg-iteration-skip-memcgs-not-yet-fully-initialized
+++ a/mm/memcontrol.c
@@ -1119,10 +1119,8 @@ skip_node:
* protected by css_get and the tree walk is rcu safe.
*/
if (next_css) {
- struct mem_cgroup *mem = mem_cgroup_from_css(next_css);
-
- if (css_tryget(&mem->css))
- return mem;
+ if ((next_css->flags & CSS_ONLINE) && css_tryget(next_css))
+ return mem_cgroup_from_css(next_css);
else {
prev_css = next_css;
goto skip_node;
_
--
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