linux-kernel - Re: radix-tree.c:__lookup

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Message-ID: <4573F600.50306@yahoo.com.au>
Date:	Mon, 04 Dec 2006 21:18:40 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Frank van Maarseveen <frankvm@...nkvm.com>
CC:	linux-kernel@...r.kernel.org, WU Fengguang <wfg@...l.ustc.edu.cn>,
	Andrew Morton <akpm@...gle.com>
Subject: Re: radix-tree.c:__lookup_slot() dead code removal

Frank van Maarseveen wrote:
> Most of the code suggests that it is valid to insert a NULL item,
> possibly a zero item with pointer cast. However, in __lookup_slot()
> whether or not the slot is found seems to depend on the actual value
> of the item in one special case. But further on it doesn't make any
> difference so to remove some dead code:
> 
> --- a/lib/radix-tree.c	2006-12-03 13:23:00.000000000 +0100
> +++ b/lib/radix-tree.c	2006-12-03 17:57:03.000000000 +0100
> @@ -319,9 +319,6 @@ static inline void **__lookup_slot(struc
>  	if (index > radix_tree_maxindex(height))
>  		return NULL;
>  
> -	if (height == 0 && root->rnode)
> -		return (void **)&root->rnode;
> -
>  	shift = (height-1) * RADIX_TREE_MAP_SHIFT;
>  	slot = &root->rnode;

I would say it is not valid to insert a NULL item (because NULL
means an unsuccessful lookup, you may as well just delete the
item).

Also, I don't see how this is dead code anyway. height == 0
radix-trees are a special case and do not have a radix_tree_node
at ->rnode.

-- 
SUSE Labs, Novell Inc.
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