__d_move(): fold manipulations with ->d_child/->d_subdirs

list_del() + list_add() is a slightly pessimised list_move()
list_del() + INIT_LIST_HEAD() is a slightly pessimised list_del_init()

Interleaving those makes the resulting code even worse.  And harder to follow...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/dcache.c

@@ -2506,8 +2506,6 @@ static void __d_move(struct dentry *dentry, struct dentry *target,
 			   d_hash(dentry->d_parent, dentry->d_name.hash));
 	}
 
-	list_del(&dentry->d_u.d_child);
-	list_del(&target->d_u.d_child);
 
 	/* Switch the names.. */
 	switch_names(dentry, target);
@@ -2517,15 +2515,15 @@ static void __d_move(struct dentry *dentry, struct dentry *target,
 	if (IS_ROOT(dentry)) {
 		dentry->d_parent = target->d_parent;
 		target->d_parent = target;
-		INIT_LIST_HEAD(&target->d_u.d_child);
+		list_del_init(&target->d_u.d_child);
 	} else {
 		swap(dentry->d_parent, target->d_parent);
 
 		/* And add them back to the (new) parent lists */
-		list_add(&target->d_u.d_child, &target->d_parent->d_subdirs);
+		list_move(&target->d_u.d_child, &target->d_parent->d_subdirs);
 	}
 
-	list_add(&dentry->d_u.d_child, &dentry->d_parent->d_subdirs);
+	list_move(&dentry->d_u.d_child, &dentry->d_parent->d_subdirs);
 
 	write_seqcount_end(&target->d_seq);
 	write_seqcount_end(&dentry->d_seq);