Re: [patch v2 3/6] memcg: rework mem_cgroup_iter to use cgroup iterators

On Sun 09-12-12 11:39:50, Ying Han wrote:

On Mon, Nov 26, 2012 at 10:47 AM, Michal Hocko [off-list ref] wrote:

[...]

quoted

                if (reclaim) {
-                       iter->position = id;
+                       struct mem_cgroup *curr = memcg;
+
+                       if (last_visited)
+                               css_put(&last_visited->css);

			    ^^^^^^^^^^^
			    here

quoted

+
+                       if (css && !memcg)
+                               curr = mem_cgroup_from_css(css);
+
+                       /* make sure that the cached memcg is not removed */
+                       if (curr)
+                               css_get(&curr->css);
+                       iter->last_visited = curr;

Here we take extra refcnt for last_visited, and assume it is under
target reclaim which then calls mem_cgroup_iter_break() and we leaked
a refcnt of the target memcg css.

I think you are not right here. The extra reference is kept for
iter->last_visited and it will be dropped the next time somebody sees
the same zone-priority iter. See above.

Or have I missed your question?

[...]
-- 
Michal Hocko
SUSE Labs

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