Re: [PATCH 8/9] ublk: simplify aborting ublk request

[Uday Shankar <ushankar@purestorage.com>]

On Mon, Apr 14, 2025 at 07:25:49PM +0800, Ming Lei wrote:
> Now ublk_abort_queue() is moved to ublk char device release handler,
> meantime our request queue is "quiesced" because either ->canceling was
> set from uring_cmd cancel function or all IOs are inflight and can't be
> completed by ublk server, things becomes easy much:
> 
> - all uring_cmd are done, so we needn't to mark io as UBLK_IO_FLAG_ABORTED
> for handling completion from uring_cmd
> 
> - ublk char device is closed, no one can hold IO request reference any more,
> so we can simply complete this request or requeue it for ublk_nosrv_should_reissue_outstanding.
> 
> Signed-off-by: Ming Lei <ming.lei@redhat.com>

Reviewed-by: Uday Shankar <ushankar@purestorage.com>

> ---
>  drivers/block/ublk_drv.c | 82 ++++++++++------------------------------
>  1 file changed, 20 insertions(+), 62 deletions(-)
> 
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index f827c2ef00a9..37a0cb8011c1 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -122,15 +122,6 @@ struct ublk_uring_cmd_pdu {
>   */
>  #define UBLK_IO_FLAG_OWNED_BY_SRV 0x02
>  
> -/*
> - * IO command is aborted, so this flag is set in case of
> - * !UBLK_IO_FLAG_ACTIVE.
> - *
> - * After this flag is observed, any pending or new incoming request
> - * associated with this io command will be failed immediately
> - */
> -#define UBLK_IO_FLAG_ABORTED 0x04
> -
>  /*
>   * UBLK_IO_FLAG_NEED_GET_DATA is set because IO command requires
>   * get data buffer address from ublksrv.
> @@ -1083,12 +1074,6 @@ static inline void __ublk_complete_rq(struct request *req)
>  	unsigned int unmapped_bytes;
>  	blk_status_t res = BLK_STS_OK;
>  
> -	/* called from ublk_abort_queue() code path */
> -	if (io->flags & UBLK_IO_FLAG_ABORTED) {
> -		res = BLK_STS_IOERR;
> -		goto exit;
> -	}
> -
>  	/* failed read IO if nothing is read */
>  	if (!io->res && req_op(req) == REQ_OP_READ)
>  		io->res = -EIO;
> @@ -1138,47 +1123,6 @@ static void ublk_complete_rq(struct kref *ref)
>  	__ublk_complete_rq(req);
>  }
>  
> -static void ublk_do_fail_rq(struct request *req)
> -{
> -	struct ublk_queue *ubq = req->mq_hctx->driver_data;
> -
> -	if (ublk_nosrv_should_reissue_outstanding(ubq->dev))
> -		blk_mq_requeue_request(req, false);
> -	else
> -		__ublk_complete_rq(req);
> -}
> -
> -static void ublk_fail_rq_fn(struct kref *ref)
> -{
> -	struct ublk_rq_data *data = container_of(ref, struct ublk_rq_data,
> -			ref);
> -	struct request *req = blk_mq_rq_from_pdu(data);
> -
> -	ublk_do_fail_rq(req);
> -}
> -
> -/*
> - * Since ublk_rq_task_work_cb always fails requests immediately during
> - * exiting, __ublk_fail_req() is only called from abort context during
> - * exiting. So lock is unnecessary.
> - *
> - * Also aborting may not be started yet, keep in mind that one failed
> - * request may be issued by block layer again.
> - */
> -static void __ublk_fail_req(struct ublk_queue *ubq, struct ublk_io *io,
> -		struct request *req)
> -{
> -	WARN_ON_ONCE(io->flags & UBLK_IO_FLAG_ACTIVE);
> -
> -	if (ublk_need_req_ref(ubq)) {
> -		struct ublk_rq_data *data = blk_mq_rq_to_pdu(req);
> -
> -		kref_put(&data->ref, ublk_fail_rq_fn);
> -	} else {
> -		ublk_do_fail_rq(req);
> -	}
> -}
> -
>  static void ubq_complete_io_cmd(struct ublk_io *io, int res,
>  				unsigned issue_flags)
>  {
> @@ -1670,10 +1614,26 @@ static void ublk_commit_completion(struct ublk_device *ub,
>  		ublk_put_req_ref(ubq, req);
>  }
>  
> +static void __ublk_fail_req(struct ublk_queue *ubq, struct ublk_io *io,
> +		struct request *req)
> +{
> +	WARN_ON_ONCE(io->flags & UBLK_IO_FLAG_ACTIVE);
> +
> +	if (ublk_nosrv_should_reissue_outstanding(ubq->dev))
> +		blk_mq_requeue_request(req, false);
> +	else {
> +		io->res = -EIO;
> +		__ublk_complete_rq(req);
> +	}
> +}
> +
>  /*
> - * Called from ubq_daemon context via cancel fn, meantime quiesce ublk
> - * blk-mq queue, so we are called exclusively with blk-mq and ubq_daemon
> - * context, so everything is serialized.
> + * Called from ublk char device release handler, when any uring_cmd is
> + * done, meantime request queue is "quiesced" since all inflight requests
> + * can't be completed because ublk server is dead.
> + *
> + * So no one can hold our request IO reference any more, simply ignore the
> + * reference, and complete the request immediately
>   */
>  static void ublk_abort_queue(struct ublk_device *ub, struct ublk_queue *ubq)
>  {
> @@ -1690,10 +1650,8 @@ static void ublk_abort_queue(struct ublk_device *ub, struct ublk_queue *ubq)
>  			 * will do it
>  			 */
>  			rq = blk_mq_tag_to_rq(ub->tag_set.tags[ubq->q_id], i);
> -			if (rq && blk_mq_request_started(rq)) {
> -				io->flags |= UBLK_IO_FLAG_ABORTED;
> +			if (rq && blk_mq_request_started(rq))
>  				__ublk_fail_req(ubq, io, rq);
> -			}
>  		}
>  	}
>  }
> -- 
> 2.47.0
>