[RFC] memory unplug v5 [2/6] isolate lru page race fix

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

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>

---
 mm/migrate.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

Index: devel-2.6.22-rc4-mm2/mm/migrate.c
===================================================================
--- devel-2.6.22-rc4-mm2.orig/mm/migrate.c
+++ devel-2.6.22-rc4-mm2/mm/migrate.c
@@ -49,9 +49,8 @@ int isolate_lru_page(struct page *page, 
 		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);

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