linux-kernel - Re: [PATCH 2/3] writeback: fix incorrect return value type of bdi_dirty

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Message-ID: <20120819021757.GB16796@localhost>
Date:	Sun, 19 Aug 2012 10:17:57 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	Namjae Jeon <linkinjeon@...il.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 2/3] writeback: fix incorrect return value type of
 bdi_dirty_limit

On Sat, Aug 18, 2012 at 05:49:21AM -0400, Namjae Jeon wrote:
> unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
> 
> Above function return type is unsigned long, but return value is
> kept in "u64 bdi_dirty".
> It can return incorrect value by type casting.

I don't see how the cast can return wrong value.
The u64 is necessary for the intermediate calculations.

Thanks,
Fengguang

> Signed-off-by: Namjae Jeon <linkinjeon@...il.com>
> ---
>  mm/page-writeback.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 49133b6..73a7a06 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -546,7 +546,7 @@ static unsigned long hard_dirty_limit(unsigned long thresh)
>   */
>  unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
>  {
> -	u64 bdi_dirty;
> +	unsigned long bdi_dirty;
>  	long numerator, denominator;
>  
>  	/*
> -- 
> 1.7.9.5
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