2015-11-04 07:58:34

by yalin wang

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

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 <[email protected]>
---
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;
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

2015-11-05 15:40:31

by Jan Kara

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 <[email protected]>
> ---
> 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 <[email protected]>
SUSE Labs, CR