Re: [PATCH] io_uring: retry in case of short read on block device

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

On 8/21/21 4:07 PM, Ming Lei wrote:
> In case of buffered reading from block device, when short read happens,
> we should retry to read more, otherwise the IO will be completed
> partially, for example, the following fio expects to read 2MB, but it
> can only read 1M or less bytes:
> 
>     fio --name=onessd --filename=/dev/nvme0n1 --filesize=2M \
> 	--rw=randread --bs=2M --direct=0 --overwrite=0 --numjobs=1 \
> 	--iodepth=1 --time_based=0 --runtime=2 --ioengine=io_uring \
> 	--registerfiles --fixedbufs --gtod_reduce=1 --group_reporting
> 
> Fix the issue by allowing short read retry for block device, which sets
> FMODE_BUF_RASYNC really.

Should note that overhead on touching inode shouldn't be of concern at
this point, so all looks good

Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>


> Fixes: 9a173346bd9e ("io_uring: fix short read retries for non-reg files")
> Cc: Pavel Begunkov <asml.silence@gmail.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>  fs/io_uring.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index bf548af0426c..bbcd1a9e75e5 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -3268,6 +3268,12 @@ static inline int io_iter_do_read(struct io_kiocb *req, struct iov_iter *iter)
>  		return -EINVAL;
>  }
>  
> +static bool need_read_all(struct io_kiocb *req)
> +{
> +	return req->flags & REQ_F_ISREG ||
> +		S_ISBLK(file_inode(req->file)->i_mode);
> +}
> +
>  static int io_read(struct io_kiocb *req, unsigned int issue_flags)
>  {
>  	struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
> @@ -3322,7 +3328,7 @@ static int io_read(struct io_kiocb *req, unsigned int issue_flags)
>  	} else if (ret == -EIOCBQUEUED) {
>  		goto out_free;
>  	} else if (ret <= 0 || ret == io_size || !force_nonblock ||
> -		   (req->flags & REQ_F_NOWAIT) || !(req->flags & REQ_F_ISREG)) {
> +		   (req->flags & REQ_F_NOWAIT) || !need_read_all(req)) {
>  		/* read all, failed, already did sync or don't want to retry */
>  		goto done;
>  	}
> 

-- 
Pavel Begunkov