Re: [PATCH 5/6] ext4: write back partial-zeroed edges in WRITE_ZEROES

[Jan Kara]

On Wed 01-07-26 22:20:08, yizhang089@xxxxxxxxx wrote:
> From: Zhang Yi <yi.zhang@xxxxxxxxxx>
> 
> FALLOC_FL_WRITE_ZEROES requires that all blocks in the requested range
> end up as written extents with zeroed content. For unaligned edges that
> were partial-zeroed in dirty unwritten or delalloc state, the buffer
> is left dirty while the underlying extent may not yet be converted to
> written. As a result, a subsequent SYNC write to this range would still
> trigger metadata changes, which violates the semantics of WRITE_ZEROES.
> 
> Fix this by calling filemap_write_and_wait_range() for partial-zeroed
> edges to flush out the zeroed data and ensure the extent conversion
> is complete.
> 
> Fixes: f4265b8d32c4 ("ext4: add FALLOC_FL_WRITE_ZEROES support")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza

> ---
>  fs/ext4/extents.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index c34505765521..c083703bf704 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -4791,7 +4791,15 @@ static long ext4_zero_range(struct file *file, loff_t offset,
>  	if (IS_ALIGNED(offset | end, blocksize))
>  		return ret;
>  
> -	if (((file->f_flags & O_SYNC) || IS_SYNC(inode)) && partial_zeroed) {
> +	/*
> +	 * In FALLOC_FL_WRITE_ZEROES mode, edges that have been partially
> +	 * zeroed must be written back to ensure the entire zeroed range
> +	 * is converted to the written state. In SYNC mode, writeback is
> +	 * also required to persist the zeroed data to disk.
> +	 */
> +	if (partial_zeroed &&
> +	    ((mode & FALLOC_FL_WRITE_ZEROES) ||
> +	     (file->f_flags & O_SYNC) || IS_SYNC(inode))) {
>  		ret = filemap_write_and_wait_range(inode->i_mapping, offset,
>  						   end - 1);
>  		if (ret)
> -- 
> 2.53.0
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR