[PATCH v3 04/11] mm/page_alloc: protect pcp->batch accesses with ACCESS_ONCE

[Cody P Schafer <cody@linux.vnet.ibm.com>]

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>
---
 mm/page_alloc.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f2929df..9dd0dc0 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1181,10 +1181,12 @@ 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) {
@@ -1352,8 +1354,9 @@ 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:
-- 
1.8.2.1

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