Re: [PATCH] io_uring: no read-retry on -EAGAIN error and O_NONBLOCK marked file

[Pavel Begunkov <asml.silence@gmail.com>]

On 02/09/2020 19:00, Jens Axboe wrote:
>     Actually two things that need fixing up here:
>     
>     - The io_rw_reissue() -EAGAIN retry is explicit to block devices and
>       regular files, so don't ever attempt to do that on other types of
>       files.
>     
>     - If we hit -EAGAIN on a nonblock marked file, don't arm poll handler for
>       it. It should just complete with -EAGAIN.
>     
>     Cc: stable@vger.kernel.org
>     Reported-by: Norman Maurer <norman.maurer@googlemail.com>
>     Signed-off-by: Jens Axboe <axboe@kernel.dk>
> 
> ---
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index b1ccd7072d93..65656102bbeb 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -2300,8 +2300,11 @@ static bool io_resubmit_prep(struct io_kiocb *req, int error)
>  static bool io_rw_reissue(struct io_kiocb *req, long res)
>  {
>  #ifdef CONFIG_BLOCK
> +	umode_t mode = file_inode(req->file)->i_mode;
>  	int ret;
>  
> +	if (!S_ISBLK(mode) && !S_ISREG(mode))
> +		return false;
>  	if ((res != -EAGAIN && res != -EOPNOTSUPP) || io_wq_current_is_worker())
>  		return false;
>  
> @@ -3146,6 +3149,9 @@ static int io_read(struct io_kiocb *req, bool force_nonblock,
>  		/* IOPOLL retry should happen for io-wq threads */
>  		if (!force_nonblock && !(req->ctx->flags & IORING_SETUP_IOPOLL))
>  			goto done;
> +		/* no retry on NONBLOCK marked file */
> +		if (req->file->f_flags & O_NONBLOCK)
> +			goto done;

Looks like it works with open(O_NONBLOCK) but not with IOCB_NOWAIT in the
request's flags. Is that so?


>  		/* 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);
> @@ -3291,8 +3297,12 @@ static int io_write(struct io_kiocb *req, bool force_nonblock,
>  		/* IOPOLL retry should happen for io-wq threads */
>  		if ((req->ctx->flags & IORING_SETUP_IOPOLL) && ret2 == -EAGAIN)
>  			goto copy_iov;
> +done:
>  		kiocb_done(kiocb, ret2, cs);
>  	} else {
> +		/* no retry on NONBLOCK marked file */
> +		if (req->file->f_flags & O_NONBLOCK)
> +			goto done;
>  copy_iov:
>  		/* some cases will consume bytes even on error returns */
>  		iov_iter_revert(iter, iov_count - iov_iter_count(iter));
> 

-- 
Pavel Begunkov