mnt: Improve the umount_tree flags

- Remove the unneeded declaration from pnode.h
- Mark umount_tree static as it has no callers outside of namespace.c
- Define an enumeration of umount_tree's flags.
- Pass umount_tree's flags in by name

This removes the magic numbers 0, 1 and 2 making the code a little
clearer and makes it possible for there to be lazy unmounts that don't
propagate.  Which is what __detach_mounts actually wants for example.

Cc: stable@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

fs/namespace.c

@@ -1317,14 +1317,15 @@ static inline void namespace_lock(void)
 	down_write(&namespace_sem);
 }
 
+enum umount_tree_flags {
+	UMOUNT_SYNC = 1,
+	UMOUNT_PROPAGATE = 2,
+};
 /*
  * mount_lock must be held
  * namespace_sem must be held for write
- * how = 0 => just this tree, don't propagate
- * how = 1 => propagate; we know that nobody else has reference to any victims
- * how = 2 => lazy umount
  */
-void umount_tree(struct mount *mnt, int how)
+static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
 {
 	HLIST_HEAD(tmp_list);
 	struct mount *p;
@@ -1337,7 +1338,7 @@ void umount_tree(struct mount *mnt, int how)
 	hlist_for_each_entry(p, &tmp_list, mnt_hash)
 		list_del_init(&p->mnt_child);
 
-	if (how)
+	if (how & UMOUNT_PROPAGATE)
 		propagate_umount(&tmp_list);
 
 	while (!hlist_empty(&tmp_list)) {
@@ -1347,7 +1348,7 @@ void umount_tree(struct mount *mnt, int how)
 		list_del_init(&p->mnt_list);
 		__touch_mnt_namespace(p->mnt_ns);
 		p->mnt_ns = NULL;
-		if (how < 2)
+		if (how & UMOUNT_SYNC)
 			p->mnt.mnt_flags |= MNT_SYNC_UMOUNT;
 
 		pin_insert_group(&p->mnt_umount, &p->mnt_parent->mnt, &unmounted);
@@ -1445,14 +1446,14 @@ static int do_umount(struct mount *mnt, int flags)
 
 	if (flags & MNT_DETACH) {
 		if (!list_empty(&mnt->mnt_list))
-			umount_tree(mnt, 2);
+			umount_tree(mnt, UMOUNT_PROPAGATE);
 		retval = 0;
 	} else {
 		shrink_submounts(mnt);
 		retval = -EBUSY;
 		if (!propagate_mount_busy(mnt, 2)) {
 			if (!list_empty(&mnt->mnt_list))
-				umount_tree(mnt, 1);
+				umount_tree(mnt, UMOUNT_PROPAGATE|UMOUNT_SYNC);
 			retval = 0;
 		}
 	}
@@ -1484,7 +1485,7 @@ void __detach_mounts(struct dentry *dentry)
 	lock_mount_hash();
 	while (!hlist_empty(&mp->m_list)) {
 		mnt = hlist_entry(mp->m_list.first, struct mount, mnt_mp_list);
-		umount_tree(mnt, 2);
+		umount_tree(mnt, UMOUNT_PROPAGATE);
 	}
 	unlock_mount_hash();
 	put_mountpoint(mp);
@@ -1646,7 +1647,7 @@ struct mount *copy_tree(struct mount *mnt, struct dentry *dentry,
 out:
 	if (res) {
 		lock_mount_hash();
-		umount_tree(res, 0);
+		umount_tree(res, UMOUNT_SYNC);
 		unlock_mount_hash();
 	}
 	return q;
@@ -1670,7 +1671,7 @@ void drop_collected_mounts(struct vfsmount *mnt)
 {
 	namespace_lock();
 	lock_mount_hash();
-	umount_tree(real_mount(mnt), 0);
+	umount_tree(real_mount(mnt), UMOUNT_SYNC);
 	unlock_mount_hash();
 	namespace_unlock();
 }
@@ -1853,7 +1854,7 @@ static int attach_recursive_mnt(struct mount *source_mnt,
  out_cleanup_ids:
 	while (!hlist_empty(&tree_list)) {
 		child = hlist_entry(tree_list.first, struct mount, mnt_hash);
-		umount_tree(child, 0);
+		umount_tree(child, UMOUNT_SYNC);
 	}
 	unlock_mount_hash();
 	cleanup_group_ids(source_mnt, NULL);
@@ -2033,7 +2034,7 @@ static int do_loopback(struct path *path, const char *old_name,
 	err = graft_tree(mnt, parent, mp);
 	if (err) {
 		lock_mount_hash();
-		umount_tree(mnt, 0);
+		umount_tree(mnt, UMOUNT_SYNC);
 		unlock_mount_hash();
 	}
 out2:
@@ -2404,7 +2405,7 @@ void mark_mounts_for_expiry(struct list_head *mounts)
 	while (!list_empty(&graveyard)) {
 		mnt = list_first_entry(&graveyard, struct mount, mnt_expire);
 		touch_mnt_namespace(mnt->mnt_ns);
-		umount_tree(mnt, 1);
+		umount_tree(mnt, UMOUNT_PROPAGATE|UMOUNT_SYNC);
 	}
 	unlock_mount_hash();
 	namespace_unlock();
@@ -2475,7 +2476,7 @@ static void shrink_submounts(struct mount *mnt)
 			m = list_first_entry(&graveyard, struct mount,
 						mnt_expire);
 			touch_mnt_namespace(m->mnt_ns);
-			umount_tree(m, 1);
+			umount_tree(m, UMOUNT_PROPAGATE|UMOUNT_SYNC);
 		}
 	}
 }

fs/pnode.h

@@ -47,7 +47,6 @@ int get_dominating_id(struct mount *mnt, const struct path *root);
 unsigned int mnt_get_count(struct mount *mnt);
 void mnt_set_mountpoint(struct mount *, struct mountpoint *,
 			struct mount *);
-void umount_tree(struct mount *, int);
 struct mount *copy_tree(struct mount *, struct dentry *, int);
 bool is_path_reachable(struct mount *, struct dentry *,
 			 const struct path *root);