Clean follow_dotdot() up a bit

No need to open-code follow_up() in it and locking can be lighter.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -689,33 +689,20 @@ static __always_inline void follow_dotdot(struct nameidata *nd)
 	set_root(nd);
 
 	while(1) {
-		struct vfsmount *parent;
 		struct dentry *old = nd->path.dentry;
 
 		if (nd->path.dentry == nd->root.dentry &&
 		    nd->path.mnt == nd->root.mnt) {
 			break;
 		}
-		spin_lock(&dcache_lock);
 		if (nd->path.dentry != nd->path.mnt->mnt_root) {
-			nd->path.dentry = dget(nd->path.dentry->d_parent);
-			spin_unlock(&dcache_lock);
+			/* rare case of legitimate dget_parent()... */
+			nd->path.dentry = dget_parent(nd->path.dentry);
 			dput(old);
 			break;
 		}
-		spin_unlock(&dcache_lock);
-		spin_lock(&vfsmount_lock);
-		parent = nd->path.mnt->mnt_parent;
-		if (parent == nd->path.mnt) {
-			spin_unlock(&vfsmount_lock);
+		if (!follow_up(&nd->path))
 			break;
-		}
-		mntget(parent);
-		nd->path.dentry = dget(nd->path.mnt->mnt_mountpoint);
-		spin_unlock(&vfsmount_lock);
-		dput(old);
-		mntput(nd->path.mnt);
-		nd->path.mnt = parent;
 	}
 	follow_mount(&nd->path);
 }