linux-kernel - [patch v2 2/6] memcg: keep prev's css alive for the whole mem_cgroup

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 26 Nov 2012 19:47:47 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	linux-mm@...ck.org
Cc:	linux-kernel@...r.kernel.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Ying Han <yinghan@...gle.com>, Tejun Heo <htejun@...il.com>,
	Glauber Costa <glommer@...allels.com>,
	Li Zefan <lizefan@...wei.com>
Subject: [patch v2 2/6] memcg: keep prev's css alive for the whole mem_cgroup_iter

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@...e.cz>
---
 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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/