linux-kernel - Re: [PATCH V3 5/7] ublk_drv: consider recovery feature in aborting mechanism

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Date:   Tue, 20 Sep 2022 11:24:12 +0800
From:   Ziyang Zhang <ZiyangZhang@...ux.alibaba.com>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     axboe@...nel.dk, xiaoguang.wang@...ux.alibaba.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        joseph.qi@...ux.alibaba.com
Subject: Re: [PATCH V3 5/7] ublk_drv: consider recovery feature in aborting
 mechanism

On 2022/9/20 11:04, Ming Lei wrote:
> On Tue, Sep 20, 2022 at 09:49:33AM +0800, Ziyang Zhang wrote:
> 
> Follows the delta patch against patch 5 for showing the idea:
> 
> 
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index 4409a130d0b6..60c5786c4711 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -656,7 +656,8 @@ static void ublk_complete_rq(struct request *req)
>   * 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_io *io, struct request *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);
>  
> @@ -667,7 +668,10 @@ static void __ublk_fail_req(struct ublk_io *io, struct request *req)
>  				req->tag,
>  				io->flags);
>  		io->flags |= UBLK_IO_FLAG_ABORTED;
> -		blk_mq_end_request(req, BLK_STS_IOERR);
> +		if (ublk_queue_can_use_recovery_reissue(ubq))
> +			blk_mq_requeue_request(req, false);

Here is one problem:
We reset io->flags to 0 in ublk_queue_reinit() and it is called before new
ubq_daemon with FETCH_REQ is accepted. ublk_abort_queue() is not protected with
ub_mutex and it is called many times in monitor_work. So same rq may be requeued
multiple times.

With recovery disabled, there is no such problem since io->flags does not change
until ublk_dev is released.

In my patch 5 I only requeue the same rq once. So re-using ublk_abort_queue() is
hard for recovery feature.
 
> +		else
> +			blk_mq_end_request(req, BLK_STS_IOERR);
>  	}
>  }
>  
> @@ -1018,7 +1022,7 @@ static void ublk_abort_queue(struct ublk_device *ub, struct ublk_queue *ubq)
>  			 */
>  			rq = blk_mq_tag_to_rq(ub->tag_set.tags[ubq->q_id], i);
>  			if (rq)
> -				__ublk_fail_req(io, rq);
> +				__ublk_fail_req(ubq, io, rq);
>  		}
>  	}
>  	ublk_put_device(ub);
> @@ -1026,12 +1030,10 @@ static void ublk_abort_queue(struct ublk_device *ub, struct ublk_queue *ubq)
>  
>  static bool ublk_check_inflight_rq(struct request *rq, void *data)
>  {
> -	struct ublk_queue *ubq = rq->mq_hctx->driver_data;
> -	struct ublk_io *io = &ubq->ios[rq->tag];
> -	bool *busy = data;
> +	bool *idle = data;
>  
> -	if (io->flags & UBLK_IO_FLAG_ACTIVE) {
> -		*busy = true;
> +	if (blk_mq_rq_state(rq) == MQ_RQ_IN_FLIGHT) {
> +		*idle = false;
>  		return false;
>  	}
>  	return true;
> @@ -1039,16 +1041,15 @@ static bool ublk_check_inflight_rq(struct request *rq, void *data)
>  
>  static void ublk_wait_tagset_rqs_idle(struct ublk_device *ub)
>  {
> -	bool busy = false;
> +	bool idle = true;
>  
>  	WARN_ON_ONCE(!blk_queue_quiesced(ub->ub_disk->queue));
>  	while (true) {
>  		blk_mq_tagset_busy_iter(&ub->tag_set,
> -				ublk_check_inflight_rq, &busy);
> -		if (busy)
> -			msleep(UBLK_REQUEUE_DELAY_MS);
> -		else
> +				ublk_check_inflight_rq, &idle);
> +		if (idle)
>  			break;
> +		msleep(UBLK_REQUEUE_DELAY_MS);
>  	}
>  }
>  
> @@ -1069,10 +1070,7 @@ static void ublk_quiesce_queue(struct ublk_device *ub,
>  					ublk_queue_can_use_recovery_reissue(ubq) ?
>  					"requeue" : "abort",
>  					ubq->q_id, i, io->flags);
> -			if (ublk_queue_can_use_recovery_reissue(ubq))
> -				blk_mq_requeue_request(rq, false);
> -			else
> -				__ublk_fail_req(io, rq);
> +			__ublk_fail_req(ubq, io, rq);
>  		} else {
>  			pr_devel("%s: done old cmd: qid %d tag %d\n",
>  					__func__, ubq->q_id, i);
> @@ -1092,12 +1090,6 @@ static void ublk_quiesce_dev(struct ublk_device *ub)
>  	if (ub->dev_info.state != UBLK_S_DEV_LIVE)
>  		goto unlock;
>  
> -	for (i = 0; i < ub->dev_info.nr_hw_queues; i++) {
> -		struct ublk_queue *ubq = ublk_get_queue(ub, i);
> -
> -		if (!ubq_daemon_is_dying(ubq))
> -			goto unlock;
> -	}
>  	blk_mq_quiesce_queue(ub->ub_disk->queue);
>  	ublk_wait_tagset_rqs_idle(ub);
>  	pr_devel("%s: quiesce ub: dev_id %d\n",
> @@ -1129,14 +1121,13 @@ static void ublk_daemon_monitor_work(struct work_struct *work)
>  		struct ublk_queue *ubq = ublk_get_queue(ub, i);
>  
>  		if (ubq_daemon_is_dying(ubq)) {
> -			if (ublk_queue_can_use_recovery(ubq)) {
> +			if (ublk_queue_can_use_recovery(ubq))
>  				schedule_work(&ub->quiesce_work);
> -			} else {
> +			else
>  				schedule_work(&ub->stop_work);
>  
> -				/* abort queue is for making forward progress */
> -				ublk_abort_queue(ub, ubq);
> -			}
> +			/* abort queue is for making forward progress */
> +			ublk_abort_queue(ub, ubq);
>  		}
>  	}
>  
> 
> 
> 
> 
> Thanks,
> Ming