lkml.org 
[lkml]   [2013]   [Jan]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v3 2/7] memcg: keep prev's css alive for the whole mem_cgroup_iter
Date
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 <mhocko@suse.cz>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
mm/memcontrol.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e71cfde..90a3b1d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1143,12 +1143,9 @@ 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;
}

@@ -1166,7 +1163,7 @@ 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;
}
@@ -1190,8 +1187,12 @@ 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


\
 
 \ /
  Last update: 2013-01-03 19:01    [W:0.108 / U:0.932 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site