linux-kernel - [RFC][PATCH 5/4] memcg: don't call res_counter

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Message-Id: <20090114175121.275ecd59.nishimura@mxp.nes.nec.co.jp>
Date:	Wed, 14 Jan 2009 17:51:21 +0900
From:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To:	LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Li Zefan <lizf@...fujitsu.com>,
	Paul Menage <menage@...gle.com>, nishimura@....nes.nec.co.jp
Subject: [RFC][PATCH 5/4] memcg: don't call res_counter_uncharge when
 obsolete

This is a new one. Please review.

===
From: Daisuke Nishimura <nishimura@....nes.nec.co.jp>

mem_cgroup_get ensures that the memcg that has been got can be accessed
even after the directory has been removed, but it doesn't ensure that parents
of it can be accessed: parents might have been freed already by rmdir.

This causes a bug in case of use_hierarchy==1, because res_counter_uncharge
climb up the tree.

Check if the memcg is obsolete, and don't call res_counter_uncharge when obsole.

Signed-off-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
---
 mm/memcontrol.c |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index fb62b43..4ee95a8 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1182,7 +1182,8 @@ int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
 		/* avoid double counting */
 		mem = swap_cgroup_record(ent, NULL);
 		if (mem) {
-			res_counter_uncharge(&mem->memsw, PAGE_SIZE);
+			if (!mem_cgroup_is_obsolete(mem))
+				res_counter_uncharge(&mem->memsw, PAGE_SIZE);
 			mem_cgroup_put(mem);
 		}
 	}
@@ -1252,7 +1253,8 @@ void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
 		struct mem_cgroup *memcg;
 		memcg = swap_cgroup_record(ent, NULL);
 		if (memcg) {
-			res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
+			if (!mem_cgroup_is_obsolete(memcg))
+				res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
 			mem_cgroup_put(memcg);
 		}
 
@@ -1397,7 +1399,8 @@ void mem_cgroup_uncharge_swap(swp_entry_t ent)
 
 	memcg = swap_cgroup_record(ent, NULL);
 	if (memcg) {
-		res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
+		if (!mem_cgroup_is_obsolete(memcg))
+			res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
 		mem_cgroup_put(memcg);
 	}
 }
--
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