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Subject: Re: [PATCH] blk-mq: fix a hung issue when set device state to blocked
 and restore running
To:     Ming Lei <ming.lei@redhat.com>
CC:     <axboe@kernel.dk>, <hch@lst.de>, <linux-block@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <houtao1@huawei.com>,
        <yanaijie@huawei.com>, <jianchao.w.wang@oracle.com>
References: <1553068921-6605-1-git-send-email-zhengbin13@huawei.com>
 <20190320081110.GA8408@ming.t460p>
From:   "zhengbin (A)" <zhengbin13@huawei.com>
Message-ID: <c0821276-2127-e6d8-97b0-b96628d11ba7@huawei.com>
Date:   Wed, 20 Mar 2019 16:52:40 +0800
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Thanks for your quick reply, I will study BLK_STS_DEV_RESOURCE in detail

> BLK_STS_DEV_RESOURCE means that the driver will rerun hw queue, so
> maybe you need to investigate why it is returned from scsi driver first.
because we set the device state to blocked,
scsi_queue_rq-->prep_to_mq(return BLK_STS_RESOURCE)
	     -->out_put_budget  transfer BLK_STS_RESOURCE to BLK_STS_DEV_RESOURCE
In this situtation, the request does not send to the driver.


If the device use sq, when we we set the device state to blocked and test dd, it will continue to
call blk_delay_queue.


If this test case really matters for you, we should try to run the hw queues after set state
to 'running'.
--->Maybe we should call blk_mq_run_hw_queue in scsi_device_set_state?


On 2019/3/20 16:11, Ming Lei wrote:
> On Wed, Mar 20, 2019 at 04:02:01PM +0800, 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.
>>
>> 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
> 
> BLK_STS_DEV_RESOURCE means that the driver will rerun hw queue, so
> maybe you need to investigate why it is returned from scsi driver first.
> 
> BTW, I'd suggest you read the big comment on BLK_STS_DEV_RESOURCE first.
> 
> Thanks,
> Ming
> 
> .
>