mnt: In umount_tree reuse mnt_list instead of mnt_hash

umount_tree builds a list of mounts that need to be unmounted.
Utilize mnt_list for this purpose instead of mnt_hash.  This begins to
allow keeping a mount on the mnt_hash after it is unmounted, which is
necessary for a properly functioning MNT_LOCKED implementation.

The fact that mnt_list is an ordinary list makding available list_move
is nice bonus.

Cc: stable@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
diff --git a/fs/pnode.h b/fs/pnode.h
index 16afc3d..aa6d65d 100644
--- a/fs/pnode.h
+++ b/fs/pnode.h
@@ -40,7 +40,7 @@
 void change_mnt_propagation(struct mount *, int);
 int propagate_mnt(struct mount *, struct mountpoint *, struct mount *,
 		struct hlist_head *);
-int propagate_umount(struct hlist_head *);
+int propagate_umount(struct list_head *);
 int propagate_mount_busy(struct mount *, int);
 void mnt_release_group_id(struct mount *);
 int get_dominating_id(struct mount *mnt, const struct path *root);