Re: [PATCH] mm/mmap.c: remove redundant check "if (length < info->length)"

Re: [PATCH] mm/mmap.c: remove redundant check "if (length < info->length)"

[Naoya Horiguchi]

On Thu, Jan 07, 2016 at 04:59:23PM +0800, Wang Xiaoqiang wrote:
> Hi, all,
> 
> since the code:
> 
> length = info->length + info->align_mask
> 
> and all variables above are "unsigned long" type,
> so there must be "length >= info->length".

I think that if info->align_mask is "very large" as an unsigned long value
and the sum of these 2 overflows, length can become smaller than info->length,
so we seem to need the check.

But why returning -ENOMEM?  Isn't it worth VM_BUG_ON()?

Thanks,
Naoya Horiguchi

> 
> Signed-off-by: Wang Xiaoqiang <wangxq10@lzu.edu.cn>
> ---
>  mm/mmap.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 2ce04a6..99fc461 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1716,8 +1716,6 @@ unsigned long unmapped_area(struct vm_unmapped_area_info *info)
>  
>  	/* Adjust search length to account for worst case alignment overhead */
>  	length = info->length + info->align_mask;
> -	if (length < info->length)
> -		return -ENOMEM;
>  
>  	/* Adjust search limits by the desired length */
>  	if (info->high_limit < length)
> -- 
> 2.1.4
> 
> thanks,
> Wang Xiaoqiang
> 
> 
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