Re: [RFC] ext4: fix a BUG in ext4_mpage_readpages()

From: Jan Kara
Date: Thu Nov 05 2015 - 10:40:41 EST


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@xxxxxxxxx>
> ---
> 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@xxxxxxxx>
SUSE Labs, CR
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