linux-kernel - Re: [RFC PATCH] mm: memblock: fix wrong memmove size in memblock_merge

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Message-ID: <20130104145635.GA15633@mtj.dyndns.org>
Date:	Fri, 4 Jan 2013 09:56:35 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Lin Feng <linfeng@...fujitsu.com>
Cc:	akpm@...ux-foundation.org, mingo@...nel.org, yinghai@...nel.org,
	liwanp@...ux.vnet.ibm.com, benh@...nel.crashing.org,
	tangchen@...fujitsu.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] mm: memblock: fix wrong memmove size in
 memblock_merge_regions()

On Fri, Jan 04, 2013 at 05:10:50PM +0800, Lin Feng wrote:
> The memmove span covers from (next+1) to the end of the array, and the index
> of next is (i+1), so the index of (next+1) is (i+2). So the size of remaining
> array elements is (type->cnt - (i + 2)).
> 
> PS. It seems that memblock_merge_regions() could be made some improvement:
> we need't memmove the remaining array elements until we find a none-mergable
> element, but now we memmove everytime we find a neighboring compatible region.
> I'm not sure if the trial is worth though.
> 
> Cc: Tejun Heo <tj@...nel.org>
> Signed-off-by: Lin Feng <linfeng@...fujitsu.com>
> ---
>  mm/memblock.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 6259055..85ce056 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -314,7 +314,7 @@ static void __init_memblock memblock_merge_regions(struct memblock_type *type)
>  		}
>  
>  		this->size += next->size;
> -		memmove(next, next + 1, (type->cnt - (i + 1)) * sizeof(*next));
> +		memmove(next, next + 1, (type->cnt - (i + 2)) * sizeof(*next));

Heh, that's confusing.  Nice catch.  Can you please also add a comment
explaning the index so that it's less confusing for the future readers?

Thanks.

-- 
tejun
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