On Mon, Aug 24, 2020 at 11:48:44AM -0600, Jens Axboe wrote:
> Some consumers of the iov_iter will return an error, but still have
> bytes consumed in the iterator. This is an issue for -EAGAIN, since we
> rely on a sane iov_iter state across retries.
>
> Fix this by ensuring that we revert consumed bytes, if any, if the file
> operations have consumed any bytes from iterator. This is similar to what
> generic_file_read_iter() does, and is always safe as we have the previous
> bytes count handy already.
>
> Fixes: ff6165b2d7f6 ("io_uring: retain iov_iter state over io_read/io_write calls")
> Reported-by: Dmitry Shulyak <yashulyak@xxxxxxxxx>
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
>
> ---
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index c9d526ff55e0..e030b33fa53e 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -3153,6 +3153,8 @@ static int io_read(struct io_kiocb *req, bool force_nonblock,
> } else if (ret == -EAGAIN) {
> if (!force_nonblock)
> goto done;
> + /* some cases will consume bytes even on error returns */
> + iov_iter_revert(iter, iov_count - iov_iter_count(iter));
> ret = io_setup_async_rw(req, iovec, inline_vecs, iter, false);
> if (ret)
> goto out_free;
> @@ -3294,6 +3296,8 @@ static int io_write(struct io_kiocb *req, bool force_nonblock,
> if (!force_nonblock || ret2 != -EAGAIN) {
> kiocb_done(kiocb, ret2, cs);
> } else {
> + /* some cases will consume bytes even on error returns */
> + iov_iter_revert(iter, iov_count - iov_iter_count(iter));
> copy_iov:
> ret = io_setup_async_rw(req, iovec, inline_vecs, iter, false);
> if (!ret)
>
What about moving iov_iter_revert() in io_setup_async_rw(), passing
iov_initial_count as parameter?
Maybe it's out of purpose since we use it even when we're not trying again.
Anyway the patch LGTM:
Reviewed-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
Thanks,
Stefano
