Re: [PATCH 2/8] xarray: Provide xas_erase() helper

[Matthew Wilcox <willy@infradead.org>]

On Tue, Feb 04, 2020 at 03:25:08PM +0100, Jan Kara wrote:
> +void *xas_erase(struct xa_state *xas)
> +{
> +	void *entry;
> +
> +	entry = xas_store(xas, NULL);
> +	xas_init_marks(xas);
> +
> +	return entry;
> +}
> +EXPORT_SYMBOL(xas_erase);

I didn't have a test case to show this, but ...

+static noinline void check_multi_store_4(struct xarray *xa)
+{
+       XA_BUG_ON(xa, xa_marked(xa, XA_MARK_0));
+       XA_BUG_ON(xa, !xa_empty(xa));
+
+       xa_store_index(xa, 0, GFP_KERNEL);
+       xa_store_index(xa, 2, GFP_KERNEL);
+       xa_set_mark(xa, 0, XA_MARK_0);
+       xa_set_mark(xa, 2, XA_MARK_0);
+
+       xa_store_order(xa, 0, 2, NULL, GFP_KERNEL);
+       XA_BUG_ON(xa, xa_marked(xa, XA_MARK_0));
+       xa_destroy(xa);
+}

shows a problem.  Because we delete all the entries in the tree,
xas_delete_node() sets the xas->xa_node to XAS_BOUNDS.  This fixes it:

@@ -492,7 +492,6 @@ static void xas_delete_node(struct xa_state *xas)
 
                if (!parent) {
                        xas->xa->xa_head = NULL;
-                       xas->xa_node = XAS_BOUNDS;
                        return;
                }
 
(it leaves xas->xa_node set to NULL, which makes the above work correctly
because NULL is used to mean the one element at index 0 of the array)

Now I'm wondering if it's going to break anything, though.  The test suite
runs successfully, but it can't be exhaustive.