[PATCH] Fix YA bug in __page_cache_release

__page_cache_release() needs to check PG_lru inside the lock, because
page reclaim may have taken the page off the LRU while this CPU waits
on the lock.

That's three bugs in a single twenty-line function.  So far.

mm/swap.c

@@ -76,9 +76,8 @@ void lru_add_drain(void)
  */
 void __page_cache_release(struct page *page)
 {
-	BUG_ON(page_count(page) != 0);
-	if (PageLRU(page)) {
 	unsigned long flags;
+	BUG_ON(page_count(page) != 0);
 
 	spin_lock_irqsave(&_pagemap_lru_lock, flags);
 	if (TestClearPageLRU(page)) {
@@ -90,7 +89,6 @@ void __page_cache_release(struct page *page)
 	if (page_count(page) != 0)
 		page = NULL;
 	spin_unlock_irqrestore(&_pagemap_lru_lock, flags);
-	}
 	if (page)
 		__free_pages_ok(page, 0);
 }