linux-kernel - Re: [PATCH 1/1] memblock cleanup: Remove unnecessary check in memblock_find_in_range

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Date:	Wed, 14 Aug 2013 23:27:46 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Tang Chen <tangchen@...fujitsu.com>
Cc:	mingo@...hat.com, hpa@...or.com, akpm@...ux-foundation.org,
	liwanp@...ux.vnet.ibm.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] memblock cleanup: Remove unnecessary check in
 memblock_find_in_range_node()

Hello, Tang.

On Thu, Aug 15, 2013 at 11:23:19AM +0800, Tang Chen wrote:
> Furthermore, we don't need to check "if (this_end < size)" actually. Without
> this confusing check, we only waste some loops. So this patch removes the
> check.
> 
> Signed-off-by: Tang Chen <tangchen@...fujitsu.com>
> ---
>  mm/memblock.c |    3 ---
>  1 files changed, 0 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memblock.c b/mm/memblock.c
> index a847bfe..e0c626e 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -114,9 +114,6 @@ phys_addr_t __init_memblock memblock_find_in_range_node(phys_addr_t start,
>  		this_start = clamp(this_start, start, end);
>  		this_end = clamp(this_end, start, end);
>  
> -		if (this_end < size)
> -			continue;
> -
>  		cand = round_down(this_end - size, align);
>  		if (cand >= this_start)
>  			return cand;

Hmmm... maybe I'm missing something but are you sure?  "this_end -
size" can underflow and "cand >= this_start" will be true incorrectly.

Thanks.

-- 
tejun
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