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Date:   Mon, 18 Oct 2021 21:06:20 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Jiasheng Jiang <jiasheng@iscas.ac.cn>
Cc:     akpm@linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] XArray: Fix xa_to_node by adding xa_is_node
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On Tue, Oct 12, 2021 at 08:42:50AM +0000, Jiasheng Jiang wrote:
> Directly using xa_to_node may lead to the compulsory type
> conversion of unknown type,which is unsafe.
> So it might be better that adding xa_is_node before.

No.  This is test code, and it knows what it's doing.
I suppose we could add an XA_BUG_ON(xa, !xa_is_node(xa_head(xa)));
but that seems pointless.  This patch is definitely wrong.

> Fixes: 58d6ea3 ("xarray: Add XArray unconditional store operations")
> Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
> ---
>  lib/test_xarray.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/test_xarray.c b/lib/test_xarray.c
> index 8b1c318..7ad3d51 100644
> --- a/lib/test_xarray.c
> +++ b/lib/test_xarray.c
> @@ -606,8 +606,10 @@ static noinline void check_multi_store(struct xarray *xa)
>  	XA_BUG_ON(xa, xa_load(xa, 1) != xa_mk_value(0));
>  	XA_BUG_ON(xa, xa_load(xa, 2) != NULL);
>  	rcu_read_lock();
> -	XA_BUG_ON(xa, xa_to_node(xa_head(xa))->count != 2);
> -	XA_BUG_ON(xa, xa_to_node(xa_head(xa))->nr_values != 2);
> +	if (xa_is_node(xa_head(xa))) {
> +		XA_BUG_ON(xa, xa_to_node(xa_head(xa))->count != 2);
> +		XA_BUG_ON(xa, xa_to_node(xa_head(xa))->nr_values != 2);
> +	}
>  	rcu_read_unlock();
>  
>  	/* Storing adjacent to the value does not alter the value */
> -- 
> 2.7.4
>