overlayfs: fix lockdep misannotation

In an overlay directory that shadows an empty lower directory, say
/mnt/a/empty102, do:

 	touch /mnt/a/empty102/x
 	unlink /mnt/a/empty102/x
 	rmdir /mnt/a/empty102

It's actually harmless, but needs another level of nesting between
I_MUTEX_CHILD and I_MUTEX_NORMAL.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Tested-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
(cherry picked from commit d1b72cc6d8cb766c802fdc70a5edc2f0ba8a2b57)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
diff --git a/fs/namei.c b/fs/namei.c
index a047265e..0fbf150 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2473,7 +2473,7 @@
 	}
 
 	mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT);
-	mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_CHILD);
+	mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_PARENT2);
 	return NULL;
 }