linux-kernel - Re: [PATCH] xarray: Add a BUG_ON() to ensure caller is not sibling

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Message-ID: <30EECA35-4622-46B5-857D-484282E92AAF@nvidia.com>
Date: Wed, 28 May 2025 13:12:47 -0400
From: Zi Yan <ziy@...dia.com>
To: Dev Jain <dev.jain@....com>
Cc: akpm@...ux-foundation.org, willy@...radead.org,
 linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, david@...hat.com, anshuman.khandual@....com,
 ryan.roberts@....com
Subject: Re: [PATCH] xarray: Add a BUG_ON() to ensure caller is not sibling

On 28 May 2025, at 7:31, Dev Jain wrote:

> Suppose xas is pointing somewhere near the end of the multi-entry batch.
> Then it may happen that the computed slot already falls beyond the batch,
> thus breaking the loop due to !xa_is_sibling(), and computing the wrong
> order. Thus ensure that the caller is aware of this by triggering a BUG
> when the entry is a sibling entry.

Is it possible to add a test case in lib/test_xarray.c for this?
You can compile the tests with “make -C tools/testing/radix-tree”
and run “./tools/testing/radix-tree/xarray”.

>
> This patch is motivated by code inspection and not a real bug report.
>
> Signed-off-by: Dev Jain <dev.jain@....com>
> ---
> The patch applies on 6.15 kernel.
>
>  lib/xarray.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/lib/xarray.c b/lib/xarray.c
> index 9644b18af18d..0f699766c24f 100644
> --- a/lib/xarray.c
> +++ b/lib/xarray.c
> @@ -1917,6 +1917,8 @@ int xas_get_order(struct xa_state *xas)
>  	if (!xas->xa_node)
>  		return 0;
>
> +	XA_NODE_BUG_ON(xas->xa_node, xa_is_sibling(xa_entry(xas->xa,
> +		       xas->xa_node, xas->xa_offset)));
>  	for (;;) {
>  		unsigned int slot = xas->xa_offset + (1 << order);
>
> -- 
> 2.30.2


Best Regards,
Yan, Zi