mm: fix incorrect page removal from LRU

The isolated page is "cursor_page" not "page".

This could cause LRU list corruption under memory pressure, caught by
CONFIG_DEBUG_LIST.
Reported-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: NBalbir Singh <balbir@linux.vnet.ibm.com>
Tested-by: NDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

@@ -932,7 +932,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 				continue;
 			if (__isolate_lru_page(cursor_page, mode, file) == 0) {
 				list_move(&cursor_page->lru, dst);
-				mem_cgroup_del_lru(page);
+				mem_cgroup_del_lru(cursor_page);
 				nr_taken++;
 				scan++;
 			}