linux-kernel - [PATCH] memcg: avoid overflow in memcg_hierarchical_free

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Message-Id: <1289265320-7025-1-git-send-email-gthelen@google.com>
Date:	Mon,  8 Nov 2010 17:15:20 -0800
From:	Greg Thelen <gthelen@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Johannes Weiner <hannes@...xchg.org>,
	Wu Fengguang <fengguang.wu@...el.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Greg Thelen <gthelen@...gle.com>
Subject: [PATCH] memcg: avoid overflow in memcg_hierarchical_free_pages()

Use page counts rather than byte counts to avoid overflowing
unsigned long local variables.

Signed-off-by: Greg Thelen <gthelen@...gle.com>
---
 mm/memcontrol.c |   10 +++++-----
 1 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 6c7115d..b287afd 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1345,17 +1345,17 @@ memcg_hierarchical_free_pages(struct mem_cgroup *mem)
 {
 	unsigned long free, min_free;
 
-	min_free = global_page_state(NR_FREE_PAGES) << PAGE_SHIFT;
+	min_free = global_page_state(NR_FREE_PAGES);
 
 	while (mem) {
-		free = res_counter_read_u64(&mem->res, RES_LIMIT) -
-			res_counter_read_u64(&mem->res, RES_USAGE);
+		free = (res_counter_read_u64(&mem->res, RES_LIMIT) -
+			res_counter_read_u64(&mem->res, RES_USAGE)) >>
+			PAGE_SHIFT;
 		min_free = min(min_free, free);
 		mem = parent_mem_cgroup(mem);
 	}
 
-	/* Translate free memory in pages */
-	return min_free >> PAGE_SHIFT;
+	return min_free;
 }
 
 /*
-- 
1.7.3.1

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