Re: [PATCH 3/3] iomap: don't lose a failed direct I/O bio's error when zeroing the tail

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Sep 21, 2026 at 10:31:33AM +0200, Andrea Parri wrote:
> iomap_dio_bio_iter() falls through to the sub-block tail zeroing when
> the data bio submission fails, so that the rest of the block is still
> zeroed and stale data is not exposed.  The zeroing result is assigned to
> ret, which overwrites the submission error with the successful zeroing
> result (zero) and the failed write is reported as success.
> 
> Store the zeroing result separately and only use it when the data path
> did not already fail.
> 
> Fixes: 10553a91652d9 ("iomap: fix iomap_dio_zero() for fs bs > system page size")
> Cc: stable@vger.kernel.org
> Assisted-by: LLM
> Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
> ---
>  fs/iomap/direct-io.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index 8b4039d16ce89..8ae3fe64e475c 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -581,9 +581,14 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
>  	    ((dio->flags & IOMAP_DIO_WRITE) && pos >= i_size_read(inode))) {
>  		/* zero out from the end of the write to the end of the block */
>  		pad = pos & (fs_block_size - 1);
> -		if (pad)
> -			ret = iomap_dio_zero(iter, dio, pos,
> -					     fs_block_size - pad);
> +		if (pad) {
> +			ssize_t zerror;

Why ssize_t?  iomap_dio_zero returns int, right?  I may have missed
something in my absence, but AFAICT it should be:

			int ret2 = iomap_dio_zero(...);

			if (ret2 && !ret)
				ret = ret2;

--D

> +
> +			zerror = iomap_dio_zero(iter, dio, pos,
> +						fs_block_size - pad);
> +			if (!ret)
> +				ret = zerror;
> +		}
>  	}
>  out:
>  	/* Undo iter limitation to current extent */
> -- 
> 2.53.0
>