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>
---
Decide for yourself whether to take this or not. I spent quite a while
digging into a mysterious "trying to register non-static key" issue from
lockdep, which originated from the iterator returning a vmalloc'ed memcg
a moment before the res_counter_init()s had done their spin_lock_init()s.
But the backtrace was an odd one of our own mis-devising, not a charge or
reclaim or stats trace, so probably it's never been a problem for vanilla.
mm/memcontrol.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
--- mmotm/mm/memcontrol.c 2014-01-10 18:25:02.236448954 -0800
+++ linux/mm/memcontrol.c 2014-01-12 22:21:10.700570471 -0800
@@ -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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