Subject: Re: [PATCH -next] f2fs: Use div_u64*() for 64-bit divisions

From: Chao Yu <[email-masked]>
Date: Fri, 21 Jun 2019 17:54:24 +0800

Hi Geert,

Since the original patch hasn't been merged to upstream, I think we can merge
this into original patch, how do you think?

On 2019/6/20 22:38, Geert Uytterhoeven wrote:
> On 32-bit (e.g. m68k):
> 
>     fs/f2fs/gc.o: In function `f2fs_resize_fs':
>     gc.c:(.text+0x3056): undefined reference to `__umoddi3'
>     gc.c:(.text+0x30c4): undefined reference to `__udivdi3'
> 
> Fix this by using div_u64_rem() and div_u64() for 64-by-32 modulo resp.
> division operations.
> 
> Reported-by: [email-masked]
> Fixes: d2ae7494d043bfaf ("f2fs: ioctl for removing a range from F2FS")
> Signed-off-by: Geert Uytterhoeven <[email-masked]>
> ---
> This assumes BLKS_PER_SEC(sbi) is 32-bit.
> 
>     #define BLKS_PER_SEC(sbi)                                       \
> 	    ((sbi)->segs_per_sec * (sbi)->blocks_per_seg)
> 
> Notes:
>   1. f2fs_sb_info.segs_per_sec and f2fs_sb_info.blocks_per_seg are both
>      unsigned int,
>   2. The multiplication is done in 32-bit arithmetic, hence the result
>      is of type unsigned int.
>   3. Is it guaranteed that the result will always fit in 32-bit, or can
>      this overflow?
>   4. fs/f2fs/debug.c:update_sit_info() assigns BLKS_PER_SEC(sbi) to
>      unsigned long long blks_per_sec, anticipating a 64-bit value.
> ---
>  fs/f2fs/gc.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index 5b1076505ade9f84..c65f87f11de029f4 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -1438,13 +1438,15 @@ int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count)
>  	unsigned int secs;
>  	int gc_mode, gc_type;
>  	int err = 0;
> +	__u32 rem;
>  
>  	old_block_count = le64_to_cpu(F2FS_RAW_SUPER(sbi)->block_count);
>  	if (block_count > old_block_count)
>  		return -EINVAL;
>  
>  	/* new fs size should align to section size */
> -	if (block_count % BLKS_PER_SEC(sbi))
> +	div_u64_rem(block_count, BLKS_PER_SEC(sbi), &rem);
> +	if (rem)
>  		return -EINVAL;
>  
>  	if (block_count == old_block_count)
> @@ -1463,7 +1465,7 @@ int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count)
>  	freeze_bdev(sbi->sb->s_bdev);
>  
>  	shrunk_blocks = old_block_count - block_count;
> -	secs = shrunk_blocks / BLKS_PER_SEC(sbi);
> +	secs = div_u64(shrunk_blocks, BLKS_PER_SEC(sbi));
>  	spin_lock(&sbi->stat_lock);
>  	if (shrunk_blocks + valid_user_blocks(sbi) +
>  		sbi->current_reserved_blocks + sbi->unusable_block_count +
>