memcg: fix wrong pointer initialization at page migration when memcg is disabled.
KAMEZAWA Hiroyuki [Wed, 11 Nov 2009 22:26:26 +0000 (14:26 -0800)]
Lee Schermerhorn reported that he saw bad pointer dereference in
mem_cgroup_end_migration() when he disabled memcg by boot option.

memcg's page migration logic works as

mem_cgroup_prepare_migration(page, &ptr);
do page migration
mem_cgroup_end_migration(page, ptr);

Now, ptr is not initialized in prepare_migration when memcg is disabled
by boot option. This causes panic in end_migration. This patch fixes it.

Reported-by: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/migrate.c

index 1a4bf48..7dbcb22 100644 (file)
@@ -602,7 +602,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
        struct page *newpage = get_new_page(page, private, &result);
        int rcu_locked = 0;
        int charge = 0;
-       struct mem_cgroup *mem;
+       struct mem_cgroup *mem = NULL;
 
        if (!newpage)
                return -ENOMEM;