linux-kernel - [PATCH 1/2] memcg: fix double free and make refcnt sane

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Date:	Thu, 18 Dec 2008 17:58:10 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"menage@...gle.com" <menage@...gle.com>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"lizf@...fujitsu.com" <lizf@...fujitsu.com>
Subject: [PATCH 1/2] memcg: fix double free and make refcnt sane


From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

 1. Fix double-free BUG in error route of mem_cgroup_create().
    mem_cgroup_free() itself frees per-zone-info.
 2. Making refcnt of memcg simple.
    Add 1 refcnt at creation and call free when refcnt goes down to 0.

Reviewed-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Singed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---
Index: mmotm-2.6.28-Dec16/mm/memcontrol.c
===================================================================
--- mmotm-2.6.28-Dec16.orig/mm/memcontrol.c
+++ mmotm-2.6.28-Dec16/mm/memcontrol.c
@@ -2085,14 +2085,10 @@ static struct mem_cgroup *mem_cgroup_all
  * Removal of cgroup itself succeeds regardless of refs from swap.
  */
 
-static void mem_cgroup_free(struct mem_cgroup *mem)
+static void __mem_cgroup_free(struct mem_cgroup *mem)
 {
 	int node;
 
-	if (atomic_read(&mem->refcnt) > 0)
-		return;
-
-
 	for_each_node_state(node, N_POSSIBLE)
 		free_mem_cgroup_per_zone_info(mem, node);
 
@@ -2109,11 +2105,8 @@ static void mem_cgroup_get(struct mem_cg
 
 static void mem_cgroup_put(struct mem_cgroup *mem)
 {
-	if (atomic_dec_and_test(&mem->refcnt)) {
-		if (!mem->obsolete)
-			return;
-		mem_cgroup_free(mem);
-	}
+	if (atomic_dec_and_test(&mem->refcnt))
+		__mem_cgroup_free(mem);
 }
 
 
@@ -2163,12 +2156,10 @@ mem_cgroup_create(struct cgroup_subsys *
 
 	if (parent)
 		mem->swappiness = get_swappiness(parent);
-
+	atomic_set(&mem->refcnt, 1);
 	return &mem->css;
 free_out:
-	for_each_node_state(node, N_POSSIBLE)
-		free_mem_cgroup_per_zone_info(mem, node);
-	mem_cgroup_free(mem);
+	__mem_cgroup_free(mem);
 	return ERR_PTR(-ENOMEM);
 }
 
@@ -2183,7 +2174,7 @@ static void mem_cgroup_pre_destroy(struc
 static void mem_cgroup_destroy(struct cgroup_subsys *ss,
 				struct cgroup *cont)
 {
-	mem_cgroup_free(mem_cgroup_from_cont(cont));
+	mem_cgroup_put(mem_cgroup_from_cont(cont));
 }
 
 static int mem_cgroup_populate(struct cgroup_subsys *ss,

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