Re: [PATCH] fs: RWF_NOWAIT should imply IOCB_NOIO

[Dave Chinner]

On Mon, Aug 10, 2020 at 06:48:19PM -0600, Jens Axboe wrote:
> With the change allowing read-ahead for IOCB_NOWAIT, we changed the
> RWF_NOWAIT semantics of only doing cached reads. Since we know have
> IOCB_NOIO to manage that specific side of it, just make RWF_NOWAIT
> imply IOCB_NOIO as well to restore the previous behavior.
> 
> Fixes: 2e85abf053b9 ("mm: allow read-ahead with IOCB_NOWAIT set")
> Reported-by: Dave Chinner <david@xxxxxxxxxxxxx>
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
> 
> ---
> 
> This was a known change with the buffered async read change, but we
> didn't have IOCB_NOIO until late in 5.8. Now that bases are synced,
> make the change to make RWF_NOWAIT behave like past kernels.
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index bd7ec3eaeed0..f1cca4bfdd7b 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3293,7 +3293,7 @@ static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
>  	if (flags & RWF_NOWAIT) {
>  		if (!(ki->ki_filp->f_mode & FMODE_NOWAIT))
>  			return -EOPNOTSUPP;
> -		kiocb_flags |= IOCB_NOWAIT;
> +		kiocb_flags |= IOCB_NOWAIT | IOCB_NOIO;
>  	}
>  	if (flags & RWF_HIPRI)
>  		kiocb_flags |= IOCB_HIPRI;

Looks good.

Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx>

-- 
Dave Chinner
david@xxxxxxxxxxxxx