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Subject: Re: [PATCH] blk-mq: fix a hung issue when set device state to blocked
 and restore running
To:     zhengbin <zhengbin13@huawei.com>, axboe@kernel.dk,
        ming.lei@redhat.com, hch@lst.de, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     houtao1@huawei.com, yanaijie@huawei.com, yuyufen@huawei.com
References: <1553068921-6605-1-git-send-email-zhengbin13@huawei.com>
From:   "jianchao.wang" <jianchao.w.wang@oracle.com>
Message-ID: <1e3643aa-6ce6-ddc0-721d-3c80e228a182@oracle.com>
Date:   Wed, 20 Mar 2019 16:15:30 +0800
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Hi Bin

On 3/20/19 4:02 PM, zhengbin wrote:
> When I use dd test a SCSI device which use blk-mq in the following steps:
> 1.echo "blocked" >/sys/block/sda/device/state
> 2.dd if=/dev/sda of=/mnt/t.log bs=1M count=10
> 3.echo "running" >/sys/block/sda/device/state
> dd should finish this work after step 3, unfortunately, still hung.

If this test case really matters for you, we should try to run the hw queues after set state
to 'running'.

Thanks
Jianchao
> 
> After step2, the key code process is like this:
> blk_mq_dispatch_rq_list-->scsi_queue_rq-->prep_to_mq
>                        -->if ret is BLK_STS_RESOURCE, delay run hw queue
> 
> prep_to_mq will return BLK_STS_RESOURCE, and scsi_queue_rq will transter
> it to BLK_STS_DEV_RESOURCE. In this situtation, we should delay run hw
> queue. This patch fixes that.
> 
> Fixes: 86ff7c2a80cd ("blk-mq: introduce BLK_STS_DEV_RESOURCE")
> Signed-off-by: zhengbin <zhengbin13@huawei.com>
> ---
>  block/blk-mq.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index a9c1816..556d606 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1309,15 +1309,17 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
>  		 *   returning BLK_STS_RESOURCE. Two exceptions are scsi-mq
>  		 *   and dm-rq.
>  		 *
> -		 * If driver returns BLK_STS_RESOURCE and SCHED_RESTART
> -		 * bit is set, run queue after a delay to avoid IO stalls
> -		 * that could otherwise occur if the queue is idle.
> +		 * If driver returns BLK_STS_RESOURCE or BLK_STS_DEV_RESOURCE
> +		 * and SCHED_RESTART bit is set, run queue after a delay to
> +		 * avoid IO stalls that could otherwise occur if the queue
> +		 * is idle.
>  		 */
>  		needs_restart = blk_mq_sched_needs_restart(hctx);
>  		if (!needs_restart ||
>  		    (no_tag && list_empty_careful(&hctx->dispatch_wait.entry)))
>  			blk_mq_run_hw_queue(hctx, true);
> -		else if (needs_restart && (ret == BLK_STS_RESOURCE))
> +		else if (needs_restart && ((ret == BLK_STS_RESOURCE) ||
> +					   (ret == BLK_STS_DEV_RESOURCE)))
>  			blk_mq_delay_run_hw_queue(hctx, BLK_MQ_RESOURCE_DELAY);
> 
>  		blk_mq_update_dispatch_busy(hctx, true);
> --
> 2.7.4
> 
>