From: Cody P Schafer <cody@linux.vnet.ibm.com>
Date: Wed, 19 Jun 2013 00:05:53 +0000 (+1000)
Subject: mm/page_alloc: protect pcp->batch accesses with ACCESS_ONCE
X-Git-Tag: next-20130619~2^2~555
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=e17015b6ff936245cfcd8f30e7fdd032ec475518;p=karo-tx-linux.git

mm/page_alloc: protect pcp->batch accesses with ACCESS_ONCE

pcp->batch could change at any point, avoid relying on it being a stable
value.

Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com>
Cc: Gilad Ben-Yossef <gilad@benyossef.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index eaaef2a09424..97b8f861e63d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1182,10 +1182,12 @@ void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp)
 {
 	unsigned long flags;
 	int to_drain;
+	unsigned long batch;
 
 	local_irq_save(flags);
-	if (pcp->count >= pcp->batch)
-		to_drain = pcp->batch;
+	batch = ACCESS_ONCE(pcp->batch);
+	if (pcp->count >= batch)
+		to_drain = batch;
 	else
 		to_drain = pcp->count;
 	if (to_drain > 0) {
@@ -1353,8 +1355,9 @@ void free_hot_cold_page(struct page *page, int cold)
 		list_add(&page->lru, &pcp->lists[migratetype]);
 	pcp->count++;
 	if (pcp->count >= pcp->high) {
-		free_pcppages_bulk(zone, pcp->batch, pcp);
-		pcp->count -= pcp->batch;
+		unsigned long batch = ACCESS_ONCE(pcp->batch);
+		free_pcppages_bulk(zone, batch, pcp);
+		pcp->count -= batch;
 	}
 
 out: