Re: [PATCH v2] dax: fix wrong error code returned from dax_dedupe_file_range_compare()

[Brian Foster <bfoster@redhat.com>]

On Mon, Oct 12, 2026 at 10:49:24PM +0800, jianyungao89@gmail.com wrote:
> From: Jianyun Gao <jianyungao89@gmail.com>
> 
> When dax_range_compare_iter() returns a negative error code (e.g. -EIO),
> dax_dedupe_file_range_compare() incorrectly returns 'ret' which holds the
> positive return value from iomap_iter() indicating more iterations remain.
> This positive value leaks to the caller, where vfs_dedupe_file_range()
> interprets it as success (bytes_deduped = len), causing userspace to
> incorrectly believe deduplication completed.
> 
> Return 'status' instead to propagate the actual error code.
> 
> Fixes: 39eb05112987 ("dax: advance the iomap_iter on dedupe range")

Hmm.. the patch looks fine to me, but the above commit basically just
renamed compared to status in this function. I.e. before that commit we
did:

	if (compared < 0)
		return ret;

... which seems to me has the same problem. So I'm a little curious if
either the Fixes: is wrong, or I'm just missing something..?

Brian

> Cc: stable@vger.kernel.org
> Signed-off-by: Jianyun Gao <jianyungao89@gmail.com>
> Reviewed-by: Jan Kara <jack@suse.cz>
> ---
> 
> Changes in v2:
> - Add Fixes tag and Cc stable
> - Add Reviewed-by tag from Jan Kara
> 
> v1: Link: https://lore.kernel.org/lkml/20261010021010.19575-1-jianyungao89@gmail.com/
> 
>  fs/dax.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index 6ba50142eeb2..1f6a4fbb97bd 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -2261,7 +2261,7 @@ int dax_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
>  		status = dax_range_compare_iter(&src_iter, &dst_iter,
>  				min(src_iter.len, dst_iter.len), same);
>  		if (status < 0)
> -			return ret;
> +			return status;
>  		src_iter.status = dst_iter.status = status;
>  	}
>  	return ret;
> -- 
> 2.34.1
>