[PATCH] md: prevent oops when drive set faulty in inactive md array.

hot_add_disk and hot_remove_disk check mddev->pers before proceeding.
set_disk_faulty should too.
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/md/md.c

@@ -2441,6 +2441,9 @@ static int set_disk_faulty(mddev_t *mddev, dev_t dev)
 {
 	mdk_rdev_t *rdev;
 
+	if (mddev->pers == NULL)
+		return -ENODEV;
+
 	rdev = find_rdev(mddev, dev);
 	if (!rdev)
 		return -ENODEV;