vmscan: protect zone rotation stats by lru lock

The zone's rotation statistics must not be accessed without the
corresponding LRU lock held.  Fix an unprotected write in
shrink_active_list().

Acked-by: Rik van Riel <riel@redhat.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Johannes Weiner <hannes@saeurebad.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7ea1440..62e7f62 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1248,6 +1248,7 @@ static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
                list_add(&page->lru, &l_inactive);
        }
 
+       spin_lock_irq(&zone->lru_lock);
        /*
         * Count referenced pages from currently used mappings as
         * rotated, even though they are moved to the inactive list.
@@ -1263,7 +1264,6 @@ static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
 
        pgmoved = 0;
        lru = LRU_BASE + file * LRU_FILE;
-       spin_lock_irq(&zone->lru_lock);
        while (!list_empty(&l_inactive)) {
                page = lru_to_page(&l_inactive);
                prefetchw_prev_lru_page(page, &l_inactive, flags);