[PATCH] md: define and use safe_put_page for md

md sometimes call put_page on NULL pointers (treating it like kfree).  This is
not safe, so define and use a 'safe_put_page' which checks for NULL.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/drivers/md/raid6main.c b/drivers/md/raid6main.c
index 950e5fa..06b32bd 100644
--- a/drivers/md/raid6main.c
+++ b/drivers/md/raid6main.c
@@ -2072,8 +2072,7 @@
 abort:
 	if (conf) {
 		print_raid6_conf(conf);
-		if (conf->spare_page)
-			put_page(conf->spare_page);
+		safe_put_page(conf->spare_page);
 		kfree(conf->stripe_hashtbl);
 		kfree(conf);
 	}