Re: [PATCH] iomap: turn the byte variable in iomap_zero_iter into a ssize_t

[Matthew Wilcox <willy@infradead.org>]

Dan, why is this erroneous commit still in your tree?
iomap_write_end() cannot return an errno; if an error occurs, it
returns zero.  The code in iomap_zero_iter() should be:

                bytes = iomap_write_end(iter, pos, bytes, bytes, page);
                if (WARN_ON_ONCE(bytes == 0))
                        return -EIO;

On Wed, Dec 08, 2021 at 10:12:03AM +0100, Christoph Hellwig wrote:
> bytes also hold the return value from iomap_write_end, which can contain
> a negative error value.  As bytes is always less than the page size even
> the signed type can hold the entire possible range.
> 
> Fixes: c6f40468657d ("fsdax: decouple zeroing from the iomap buffered I/O code")
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/iomap/buffered-io.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index b1511255b4df8..ac040d607f4fe 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -883,7 +883,7 @@ static loff_t iomap_zero_iter(struct iomap_iter *iter, bool *did_zero)
>  
>  	do {
>  		unsigned offset = offset_in_page(pos);
> -		size_t bytes = min_t(u64, PAGE_SIZE - offset, length);
> +		ssize_t bytes = min_t(u64, PAGE_SIZE - offset, length);
>  		struct page *page;
>  		int status;
>  
> -- 
> 2.30.2
>