switch try_to_unlazy_next() to __legitimize_mnt()

The tricky case (__legitimize_mnt() failing after having grabbed
a reference) can be trivially dealt with by leaving nd->path.mnt
non-NULL, for terminate_walk() to drop it.

legitimize_mnt() becomes static after that.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/mount.h

@@ -100,7 +100,6 @@ static inline int is_mounted(struct vfsmount *mnt)
 extern struct mount *__lookup_mnt(struct vfsmount *, struct dentry *);
 
 extern int __legitimize_mnt(struct vfsmount *, unsigned);
-extern bool legitimize_mnt(struct vfsmount *, unsigned);
 
 static inline bool __path_is_mountpoint(const struct path *path)
 {

fs/namei.c

@@ -799,13 +799,18 @@ static bool try_to_unlazy(struct nameidata *nd)
  */
 static bool try_to_unlazy_next(struct nameidata *nd, struct dentry *dentry, unsigned seq)
 {
+	int res;
 	BUG_ON(!(nd->flags & LOOKUP_RCU));
 
 	nd->flags &= ~LOOKUP_RCU;
 	if (unlikely(!legitimize_links(nd)))
 		goto out2;
-	if (unlikely(!legitimize_mnt(nd->path.mnt, nd->m_seq)))
+	res = __legitimize_mnt(nd->path.mnt, nd->m_seq);
+	if (unlikely(res)) {
+		if (res > 0)
 			goto out2;
+		goto out1;
+	}
 	if (unlikely(!lockref_get_not_dead(&nd->path.dentry->d_lockref)))
 		goto out1;
 

fs/namespace.c

@@ -648,7 +648,7 @@ int __legitimize_mnt(struct vfsmount *bastard, unsigned seq)
 }
 
 /* call under rcu_read_lock */
-bool legitimize_mnt(struct vfsmount *bastard, unsigned seq)
+static bool legitimize_mnt(struct vfsmount *bastard, unsigned seq)
 {
 	int res = __legitimize_mnt(bastard, seq);
 	if (likely(!res))