Re: BUG_ON(!mapping_empty(&inode->i_data))

[Matthew Wilcox]

On Fri, Apr 02, 2021 at 04:13:05AM +0100, Matthew Wilcox wrote:
> +     for (;;) {
> +             xas_load(xas);
> +             if (!xas_is_node(xas))
> +                     break;
> +             xas_delete_node(xas);
> +             xas->xa_index -= XA_CHUNK_SIZE;
> +             if (xas->xa_index < index)
> +                     break;

That's a bug.  index can be 0, so the condition would never be true.
It should be:

                if (xas->xa_index <= (index | XA_CHUNK_MASK))
                        break;
                xas->xa_index -= XA_CHUNK_SIZE;

The test doesn't notice this bug because the tree is otherwise empty,
and the !xas_is_node(xas) condition is hit first.  The next test will
notice this.