get rid of the last LOOKUP_RCU dependencies in link_path_walk()

New helper: terminate_walk().  An error has happened during pathname
resolution and we either drop nd->path or terminate RCU, depending
the mode we had been in.  After that, nd is essentially empty.
Switch link_path_walk() to using that for cleanup.

Now the top-level logics in link_path_walk() is back to sanity.  RCU
dependencies are in the lower-level functions.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namei.c

@@ -1343,6 +1343,18 @@ static inline int handle_dots(struct nameidata *nd, int type)
 	return 0;
 }
 
+static void terminate_walk(struct nameidata *nd)
+{
+	if (!(nd->flags & LOOKUP_RCU)) {
+		path_put(&nd->path);
+	} else {
+		nd->flags &= ~LOOKUP_RCU;
+		nd->root.mnt = NULL;
+		rcu_read_unlock();
+		br_read_unlock(vfsmount_lock);
+	}
+}
+
 /*
  * Name resolution.
  * This is the basic name resolution function, turning a pathname into
@@ -1482,14 +1494,7 @@ static int link_path_walk(const char *name, struct nameidata *nd)
 		nd->last_type = type;
 		return 0;
 	}
-	if (!(nd->flags & LOOKUP_RCU))
-		path_put(&nd->path);
-	if (nd->flags & LOOKUP_RCU) {
-		nd->flags &= ~LOOKUP_RCU;
-		nd->root.mnt = NULL;
-		rcu_read_unlock();
-		br_read_unlock(vfsmount_lock);
-	}
+	terminate_walk(nd);
 	return err;
 }