linux-kernel - Re: [PATCH 6/9] maple_tree: Remove a confusing check

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Date:   Tue, 25 Apr 2023 12:23:44 -0400
From:   "Liam R. Howlett" <Liam.Howlett@...cle.com>
To:     Peng Zhang <zhangpeng.00@...edance.com>
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, maple-tree@...ts.infradead.org
Subject: Re: [PATCH 6/9] maple_tree: Remove a confusing check

* Peng Zhang <zhangpeng.00@...edance.com> [230425 07:05]:
> After this loop, we are at the last slot of a node. Our purpose is to
> find an entry that is not NULL, but the pivot is checked here, delete
> it, and change to mas_logical_pivot() to get the pivot. Finally, only
> check whether the entry is NULL.
> 
> Why is this confusing? If the pivot is equal to 0, but if the entry is
> not NULL at this time, it will return NULL because of the pivot, but it
> should not do this, the entry is valid.

Please avoid titles that don't say much at all.. and it's borderline
insulting. I could go into the reasons this was written this way, but
that would be a waste of time.. which is another reason to focus on what
you did in your commit message.

I've removed this function entirely in my patch set, so this isn't
needed.

> 
> Signed-off-by: Peng Zhang <zhangpeng.00@...edance.com>
> ---
>  lib/maple_tree.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index 7f4b2ce84ce61..83441ef2e1f57 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -4742,17 +4742,13 @@ static inline void *mas_next_nentry(struct ma_state *mas,
>  		return NULL;
>  	}
>  
> -	pivot = mas_safe_pivot(mas, pivots, mas->offset, type);
> +	pivot = mas_logical_pivot(mas, pivots, mas->offset, type);
>  	entry = mas_slot(mas, slots, mas->offset);
>  	if (ma_dead_node(node))
>  		return NULL;
>  
> -	if (!pivot)
> -		return NULL;
> -
>  	if (!entry)
>  		return NULL;
> -
>  found:
>  	mas->last = pivot;
>  	return entry;
> -- 
> 2.20.1
>