linux-kernel - Re: [RFC] ext4: fix a BUG in ext4_mpage

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Message-ID: <20151105154031.GC23628@quack.suse.cz>
Date:	Thu, 5 Nov 2015 16:40:31 +0100
From:	Jan Kara <jack@...e.cz>
To:	yalin wang <yalin.wang2010@...il.com>
Cc:	tytso@....edu, adilger.kernel@...ger.ca,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC] ext4: fix a BUG in ext4_mpage_readpages()

On Wed 04-11-15 15:58:34, yalin wang wrote:
> The last block should be the total read pages last block,
> need adjust the block number when caculate every page.
> 
> Signed-off-by: yalin wang <yalin.wang2010@...il.com>
> ---
>  fs/ext4/readpage.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/readpage.c b/fs/ext4/readpage.c
> index 5dc5e95..d20c39d 100644
> --- a/fs/ext4/readpage.c
> +++ b/fs/ext4/readpage.c
> @@ -174,7 +174,7 @@ int ext4_mpage_readpages(struct address_space *mapping,
>  			goto confused;
>  
>  		block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
> -		last_block = block_in_file + nr_pages * blocks_per_page;
> +		last_block = block_in_file + (nr_pages - page_idx) * blocks_per_page;

I don't think your patch is correct. The for loop decrements nr_pages at each
iteration so the original code looks fine... Or which problems do you
observe?

								Honza

>  		last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
>  		if (last_block > last_block_in_file)
>  			last_block = last_block_in_file;
> -- 
> 1.9.1
> 
> --
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-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR
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