linux-kernel - [PATCH 7/9] memcg: don't need to get a reference to the parent

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 for Android: free password hash cracker in your pocket

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

Date:	Fri, 17 May 2013 15:04:42 +0800
From:	Li Zefan <lizefan@...wei.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Tejun Heo <tj@...nel.org>, Glauber Costa <glommer@...allels.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Cgroups <cgroups@...r.kernel.org>, <linux-mm@...ck.org>
Subject: [PATCH 7/9] memcg: don't need to get a reference to the parent

The cgroup core guarantees it's always safe to access the parent.

v2:
- added a comment in mem_cgroup_put() as suggested by Michal
- removed mem_cgroup_get(), otherwise gcc will warn that it's not used

Signed-off-by: Li Zefan <lizefan@...wei.com>
Acked-by: Michal Hocko <mhocko@...e.cz>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---
 mm/memcontrol.c | 19 +++----------------
 1 file changed, 3 insertions(+), 16 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index b11ea88..c6d267a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -508,7 +508,6 @@ enum res_type {
  */
 static DEFINE_MUTEX(memcg_create_mutex);
 
-static void mem_cgroup_get(struct mem_cgroup *memcg);
 static void mem_cgroup_put(struct mem_cgroup *memcg);
 
 static inline
@@ -6171,19 +6170,10 @@ static void free_rcu(struct rcu_head *rcu_head)
 	schedule_work(&memcg->work_freeing);
 }
 
-static void mem_cgroup_get(struct mem_cgroup *memcg)
-{
-	atomic_inc(&memcg->refcnt);
-}
-
 static void __mem_cgroup_put(struct mem_cgroup *memcg, int count)
 {
-	if (atomic_sub_and_test(count, &memcg->refcnt)) {
-		struct mem_cgroup *parent = parent_mem_cgroup(memcg);
+	if (atomic_sub_and_test(count, &memcg->refcnt))
 		call_rcu(&memcg->rcu_freeing, free_rcu);
-		if (parent)
-			mem_cgroup_put(parent);
-	}
 }
 
 static void mem_cgroup_put(struct mem_cgroup *memcg)
@@ -6286,12 +6276,9 @@ mem_cgroup_css_online(struct cgroup *cont)
 		res_counter_init(&memcg->kmem, &parent->kmem);
 
 		/*
-		 * We increment refcnt of the parent to ensure that we can
-		 * safely access it on res_counter_charge/uncharge.
-		 * This refcnt will be decremented when freeing this
-		 * mem_cgroup(see mem_cgroup_put).
+		 * No need to take a reference to the parent because cgroup
+		 * core guarantees its existence.
 		 */
-		mem_cgroup_get(parent);
 	} else {
 		res_counter_init(&memcg->res, NULL);
 		res_counter_init(&memcg->memsw, NULL);
-- 
1.8.0.2
--
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/