Update from upstream with manual merge of Yasunori Goto's

changes to swiotlb.c made in commit 281dd25cdc0d6903929b79183816d151ea626341
since this file has been moved from arch/ia64/lib/swiotlb.c to
lib/swiotlb.c

Signed-off-by: Tony Luck <tony.luck@intel.com>

1 files changed, 9 insertions, 4 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0ea71e887bb6..64f9570cff56 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -511,10 +511,11 @@ static int shrink_list(struct list_head *page_list, struct scan_control *sc)
                  * PageDirty _after_ making sure that the page is freeable and
                  * not in use by anybody.       (pagecache + us == 2)
                  */
-                if (page_count(page) != 2 || PageDirty(page)) {
-                        write_unlock_irq(&mapping->tree_lock);
-                        goto keep_locked;
-                }
+                if (unlikely(page_count(page) != 2))
+                        goto cannot_free;
+                smp_rmb();
+                if (unlikely(PageDirty(page)))
+                        goto cannot_free;
 
 #ifdef CONFIG_SWAP
                 if (PageSwapCache(page)) {
@@ -538,6 +539,10 @@ free_it:
                         __pagevec_release_nonlru(&freed_pvec);
                 continue;
 
+cannot_free:
+                write_unlock_irq(&mapping->tree_lock);
+                goto keep_locked;
+
 activate_locked:
                 SetPageActive(page);
                 pgactivate++;