memory unplug: isolate_lru_page fix

release_pages() in mm/swap.c changes page_count() to be 0 without removing
PageLRU flag...

This means isolate_lru_page() can see a page, PageLRU() &&
page_count(page)==0..  This is BUG.  (get_page() will be called against
count=0 page.)

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 2 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
index c8d87221f368..37c73b902008 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -49,9 +49,8 @@ int isolate_lru_page(struct page *page, struct list_head *pagelist)
                 struct zone *zone = page_zone(page);
 
                 spin_lock_irq(&zone->lru_lock);
-                if (PageLRU(page)) {
+                if (PageLRU(page) && get_page_unless_zero(page)) {
                         ret = 0;
-                        get_page(page);
                         ClearPageLRU(page);
                         if (PageActive(page))
                                 del_page_from_active_list(zone, page);