[PATCH] ext4: fix an off-by-one issue during moving extents

[PATCH] ext4: fix an off-by-one issue during moving extents

[Zhang Yi]

From: Zhang Yi <yi.zhang@huawei.com>

During the movement of a written extent, mext_page_mkuptodate() is
called to read data in the range [from, to) into the page cache and to
update the corresponding buffers. Therefore, we should not wait on any
buffer whose start offset is >= 'to'. Otherwise, it will return -EIO and
fail the extents movement.

 $ for i in `seq 3 -1 0`; \
   do xfs_io -fs -c "pwrite -b 1024 $((i * 1024)) 1024" /mnt/foo; \
   done
 $ umount /mnt && mount /dev/pmem1s /mnt  # drop cache
 $ e4defrag /mnt/foo
   e4defrag 1.47.0 (5-Feb-2023)
   ext4 defragmentation for /mnt/foo
   [1/1]/mnt/foo:    0%    [ NG ]
   Success:                       [0/1]

Fixes: a40759fb16ae ("ext4: remove array of buffer_heads from mext_page_mkuptodate()")
Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
 fs/ext4/move_extent.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
index adae3caf175a..4b091c21908f 100644
--- a/fs/ext4/move_extent.c
+++ b/fs/ext4/move_extent.c
@@ -225,7 +225,7 @@ static int mext_page_mkuptodate(struct folio *folio, size_t from, size_t to)
 	do {
 		if (bh_offset(bh) + blocksize <= from)
 			continue;
-		if (bh_offset(bh) > to)
+		if (bh_offset(bh) >= to)
 			break;
 		wait_on_buffer(bh);
 		if (buffer_uptodate(bh))
-- 
2.46.1

Re: [PATCH] ext4: fix an off-by-one issue during moving extents

[Jan Kara]

On Fri 12-09-25 18:58:41, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@huawei.com>
> 
> During the movement of a written extent, mext_page_mkuptodate() is
> called to read data in the range [from, to) into the page cache and to
> update the corresponding buffers. Therefore, we should not wait on any
> buffer whose start offset is >= 'to'. Otherwise, it will return -EIO and
> fail the extents movement.
> 
>  $ for i in `seq 3 -1 0`; \
>    do xfs_io -fs -c "pwrite -b 1024 $((i * 1024)) 1024" /mnt/foo; \
>    done
>  $ umount /mnt && mount /dev/pmem1s /mnt  # drop cache
>  $ e4defrag /mnt/foo
>    e4defrag 1.47.0 (5-Feb-2023)
>    ext4 defragmentation for /mnt/foo
>    [1/1]/mnt/foo:    0%    [ NG ]
>    Success:                       [0/1]
> 
> Fixes: a40759fb16ae ("ext4: remove array of buffer_heads from mext_page_mkuptodate()")
> Signed-off-by: Zhang Yi <yi.zhang@huawei.com>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  fs/ext4/move_extent.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
> index adae3caf175a..4b091c21908f 100644
> --- a/fs/ext4/move_extent.c
> +++ b/fs/ext4/move_extent.c
> @@ -225,7 +225,7 @@ static int mext_page_mkuptodate(struct folio *folio, size_t from, size_t to)
>  	do {
>  		if (bh_offset(bh) + blocksize <= from)
>  			continue;
> -		if (bh_offset(bh) > to)
> +		if (bh_offset(bh) >= to)
>  			break;
>  		wait_on_buffer(bh);
>  		if (buffer_uptodate(bh))
> -- 
> 2.46.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH] ext4: fix an off-by-one issue during moving extents

[Theodore Ts'o]

On Fri, 12 Sep 2025 18:58:41 +0800, Zhang Yi wrote:
> During the movement of a written extent, mext_page_mkuptodate() is
> called to read data in the range [from, to) into the page cache and to
> update the corresponding buffers. Therefore, we should not wait on any
> buffer whose start offset is >= 'to'. Otherwise, it will return -EIO and
> fail the extents movement.
> 
>  $ for i in `seq 3 -1 0`; \
>    do xfs_io -fs -c "pwrite -b 1024 $((i * 1024)) 1024" /mnt/foo; \
>    done
>  $ umount /mnt && mount /dev/pmem1s /mnt  # drop cache
>  $ e4defrag /mnt/foo
>    e4defrag 1.47.0 (5-Feb-2023)
>    ext4 defragmentation for /mnt/foo
>    [1/1]/mnt/foo:    0%    [ NG ]
>    Success:                       [0/1]
> 
> [...]

Applied, thanks!

[1/1] ext4: fix an off-by-one issue during moving extents
      commit: 12e803c8827d049ae8f2c743ef66ab87ae898375

Best regards,
-- 
Theodore Ts'o <tytso@mit.edu>