linux-kernel - [PATCH] memcg: fix Bad page state after replace_page

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Date:	Wed, 18 Apr 2012 23:34:46 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Miklos Szeredi <mszeredi@...e.cz>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: [PATCH] memcg: fix Bad page state after replace_page_cache

My 9ce70c0240d0 "memcg: fix deadlock by inverting lrucare nesting" put a
nasty little bug into v3.3's version of mem_cgroup_replace_page_cache(),
sometimes used for FUSE.  Replacing __mem_cgroup_commit_charge_lrucare()
by __mem_cgroup_commit_charge(), I used the "pc" pointer set up earlier:
but it's for oldpage, and needs now to be for newpage.  Once oldpage was
freed, its PageCgroupUsed bit (cleared above but set again here) caused
"Bad page state" messages - and perhaps worse, being missed from newpage.
(I didn't find this by using FUSE, but in reusing the function for tmpfs.)

Signed-off-by: Hugh Dickins <hughd@...gle.com>
Cc: stable@...r.kernel.org [v3.3 only]
---

 mm/memcontrol.c |    1 +
 1 file changed, 1 insertion(+)

--- 3.4-rc3/mm/memcontrol.c	2012-04-15 20:47:37.151777506 -0700
+++ linux/mm/memcontrol.c	2012-04-18 22:29:18.490639511 -0700
@@ -3392,6 +3392,7 @@ void mem_cgroup_replace_page_cache(struc
 	 * the newpage may be on LRU(or pagevec for LRU) already. We lock
 	 * LRU while we overwrite pc->mem_cgroup.
 	 */
+	pc = lookup_page_cgroup(newpage);
 	__mem_cgroup_commit_charge(memcg, newpage, 1, pc, type, true);
 }

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