Re: [External] : [PATCH 03/38] xfs: fix isize update in xfs_iomap_write_unwritten to track conversion progress

[Mark Tinguely <mark.tinguely@oracle.com>]

On 8/18/26 7:12 PM, Dave Chinner wrote:
> xfs_iomap_write_unwritten() updates i_disk_size using the end of
> the entire unwritten range (offset_fsb + count_fsb) rather than the
> end of the extent that was actually converted in each iteration
> (imap.br_startoff + imap.br_blockcount).
> 
> If the conversion requires multiple iterations and a crash occurs
> partway through, recovery would replay the first transaction which
> set i_disk_size to the end of the full range. This exposes
> unwritten extents to userspace reads as zeroes rather than the
> data that was written, because those extents have not yet been
> converted from unwritten to written state.
> 
> Fix this by computing i_size from the extent that was actually
> converted (imap), so i_disk_size advances incrementally as each
> extent is converted. On crash, recovery only exposes data in
> extents that have been both written and converted.
> 
> Fixes: 84803fb78237 ("xfs: log file size updates as part of unwritten extent conversion")
> Assisted-by: LLM
> Signed-off-by: Dave Chinner <dgc@kernel.org>
> ---

Cc: stable@vger.kernel.org # v3.3+ ?

Looks good

Reviewed-by: Mark Tinguely <mark.tinguely@oracle.com>


>   fs/xfs/xfs_iomap.c | 12 ++++++++----
>   1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> index 225c3de88d03..1437ea93563c 100644
> --- a/fs/xfs/xfs_iomap.c
> +++ b/fs/xfs/xfs_iomap.c
> @@ -682,11 +682,15 @@ xfs_iomap_write_unwritten(
>   			goto error_on_bmapi_transaction;
>   
>   		/*
> -		 * Log the updated inode size as we go.  We have to be careful
> -		 * to only log it up to the actual write offset if it is
> -		 * halfway into a block.
> +		 * Update the inode size to reflect the extent that was
> +		 * converted in this iteration. We must not advance isize
> +		 * beyond the extent we just converted, otherwise a crash
> +		 * before the next conversion exposes unwritten extents
> +		 * (zeroes) to userspace instead of the written data.
> +		 * Clamp to the byte-level write end in case the converted
> +		 * extent extends past the write boundary.
>   		 */
> -		i_size = XFS_FSB_TO_B(mp, offset_fsb + count_fsb);
> +		i_size = XFS_FSB_TO_B(mp, imap.br_startoff + imap.br_blockcount);
>   		if (i_size > offset + count)
>   			i_size = offset + count;
>   		if (update_isize && i_size > i_size_read(inode))