linux-kernel - Re: [PATCH] maple_tree: should get pivots boundary by type

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Message-Id: <20230123134341.2514c269a07ad9e7989921c6@linux-foundation.org>
Date:   Mon, 23 Jan 2023 13:43:41 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Wei Yang <richard.weiyang@...il.com>
Cc:     Liam.Howlett@...cle.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>
Subject: Re: [PATCH] maple_tree: should get pivots boundary by type

On Sat, 12 Nov 2022 23:43:08 +0000 Wei Yang <richard.weiyang@...il.com> wrote:

> We should get pivots boundary by type.
> 

When fixing a bug, please always fully describe the runtime effects of
that bug.

I see from earlier review that the bug could result in overindexing
mt_pivots[], but Liam says this code isn't presently used, but
mas_alloc() calls mte_pivot(), so I'm all confused.


> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -669,12 +669,13 @@ static inline unsigned long mte_pivot(const struct maple_enode *mn,
>  				 unsigned char piv)
>  {
>  	struct maple_node *node = mte_to_node(mn);
> +	enum maple_type type = mte_node_type(mn);
>  
> -	if (piv >= mt_pivots[piv]) {
> +	if (piv >= mt_pivots[type]) {
>  		WARN_ON(1);
>  		return 0;
>  	}
> -	switch (mte_node_type(mn)) {
> +	switch (type) {
>  	case maple_arange_64:
>  		return node->ma64.pivot[piv];
>  	case maple_range_64:
> -- 
> 2.33.1
>