From a7fe942e94b2f66aa0f11d37699c0ec8155d3ad1 Mon Sep 17 00:00:00 2001
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Date: Wed, 7 Jan 2009 18:08:13 -0800
Subject: [PATCH] memcg: swapout refcnt fix

css's refcnt is dropped before end of following access.
Hold it until end of access.

Reported-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 mm/memcontrol.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 6ad309e9825f..964a70035e8f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1171,7 +1171,9 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
 	mz = page_cgroup_zoneinfo(pc);
 	unlock_page_cgroup(pc);
 
-	css_put(&mem->css);
+	/* at swapout, this memcg will be accessed to record to swap */
+	if (ctype != MEM_CGROUP_CHARGE_TYPE_SWAPOUT)
+		css_put(&mem->css);
 
 	return mem;
 
@@ -1212,6 +1214,8 @@ void mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent)
 		swap_cgroup_record(ent, memcg);
 		mem_cgroup_get(memcg);
 	}
+	if (memcg)
+		css_put(&memcg->css);
 }
 
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
-- 
2.20.1