[patch v2 2/6] memcg: keep prev's css alive for the whole mem_cgroup_iter
From: Michal Hocko <hidden>
Date: 2012-11-26 18:48:14
Also in:
lkml
Subsystem:
control group - memory resource controller (memcg), memory management, the rest · Maintainers:
Johannes Weiner, Michal Hocko, Roman Gushchin, Shakeel Butt, Andrew Morton, Linus Torvalds
css reference counting keeps the cgroup alive even though it has been already removed. mem_cgroup_iter relies on this fact and takes a reference to the returned group. The reference is then released on the next iteration or mem_cgroup_iter_break. mem_cgroup_iter currently releases the reference right after it gets the last css_id. This is correct because neither prev's memcg nor cgroup are accessed after then. This will change in the next patch so we need to hold the group alive a bit longer so let's move the css_put at the end of the function. Signed-off-by: Michal Hocko <redacted> --- mm/memcontrol.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 0e52ec9..1f5528d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c@@ -1077,12 +1077,9 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root, if (prev && !reclaim) id = css_id(&prev->css); - if (prev && prev != root) - css_put(&prev->css); - if (!root->use_hierarchy && root != root_mem_cgroup) { if (prev) - return NULL; + goto out_css_put; return root; }
@@ -1100,7 +1097,7 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root, spin_lock(&iter->iter_lock); if (prev && reclaim->generation != iter->generation) { spin_unlock(&iter->iter_lock); - return NULL; + goto out_css_put; } id = iter->position; }
@@ -1124,8 +1121,12 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root, } if (prev && !css) - return NULL; + goto out_css_put; } +out_css_put: + if (prev && prev != root) + css_put(&prev->css); + return memcg; }
--
1.7.10.4
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