linux-kernel - [PATCH] memcg: fix memcg_cache_name() to use cgroup

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Message-ID: <514A60CD.60208@huawei.com>
Date:	Thu, 21 Mar 2013 09:22:21 +0800
From:	Li Zefan <lizefan@...wei.com>
To:	Tejun Heo <tj@...nel.org>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Cgroups <cgroups@...r.kernel.org>, <linux-mm@...ck.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Glauber Costa <glommer@...allels.com>
Subject: [PATCH] memcg: fix memcg_cache_name() to use cgroup_name()

As cgroup supports rename, it's unsafe to dereference dentry->d_name
without proper vfs locks. Fix this by using cgroup_name().

Signed-off-by: Li Zefan <lizefan@...wei.com>
---

This patch depends on "cgroup: fix cgroup_path() vs rename() race",
which has been queued for 3.10.

---
 mm/memcontrol.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 53b8201..72be5c9 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3217,17 +3217,16 @@ void mem_cgroup_destroy_cache(struct kmem_cache *cachep)
 static char *memcg_cache_name(struct mem_cgroup *memcg, struct kmem_cache *s)
 {
 	char *name;
-	struct dentry *dentry;
+
+	name = (char *)__get_free_page(GFP_TEMPORARY);
+	if (!name)
+		return NULL;
 
 	rcu_read_lock();
-	dentry = rcu_dereference(memcg->css.cgroup->dentry);
+	snprintf(name, PAGE_SIZE, "%s(%d:%s)", s->name, memcg_cache_id(memcg),
+		 cgroup_name(memcg->css.cgroup));
 	rcu_read_unlock();
 
-	BUG_ON(dentry == NULL);
-
-	name = kasprintf(GFP_KERNEL, "%s(%d:%s)", s->name,
-			 memcg_cache_id(memcg), dentry->d_name.name);
-
 	return name;
 }
 
@@ -3247,7 +3246,7 @@ static struct kmem_cache *kmem_cache_dup(struct mem_cgroup *memcg,
 	if (new)
 		new->allocflags |= __GFP_KMEMCG;
 
-	kfree(name);
+	free_page((unsigned long)name);
 	return new;
 }
 
-- 
1.8.0.2
--
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