linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: use multiplication instead of division in sanity_check_raw

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Message-ID: <c02efb8b-0ee0-665f-4b33-08ee694cc659@kernel.org>
Date:   Mon, 1 Jul 2019 22:37:53 +0800
From:   Chao Yu <chao@...nel.org>
To:     Liu Song <fishland@...yun.com>, jaegeuk@...nel.org,
        yuchao0@...wei.com
Cc:     liu.song11@....com.cn, linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: use multiplication instead of division
 in sanity_check_raw_super

Hi Song,

On 2019-7-1 21:38, Liu Song via Linux-f2fs-devel wrote:
> From: Liu Song <liu.song11@....com.cn>
> 
> Use multiplication instead of division and be more
> consistent with f2fs_msg output information.
> 
> Signed-off-by: Liu Song <liu.song11@....com.cn>
> ---
>  fs/f2fs/super.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index af58b2cc21b8..eba4c0f9c347 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -2489,7 +2489,7 @@ static int sanity_check_raw_super(struct f2fs_sb_info *sbi,
>  		return 1;
>  	}
>  
> -	if ((segment_count / segs_per_sec) < total_sections) {

I think we use division intentionally to avoid potential overflow when doing
multiplication.

You can see the detailed commit message in below fixing patch:

0cfe75c5b011 ("f2fs: enhance sanity_check_raw_super() to avoid potential overflows")

Thanks,

> +	if (segment_count < (segs_per_sec * total_sections)) {
>  		f2fs_msg(sb, KERN_INFO,
>  			"Small segment_count (%u < %u * %u)",
>  			segment_count, segs_per_sec, total_sections);
>