Re: [PATCH v4] blk-mq: fix a hung issue when set device state to blocked and restore running

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On Fri, Mar 22, 2019 at 09:45:54AM +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
> 
> prep_to_mq will return BLK_STS_RESOURCE, and scsi_queue_rq will transter
> it to BLK_STS_DEV_RESOURCE, which means that driver can guarantee that
> IO dispatch will be triggered in future when the resource is available.
> Need to follow the rule if we set the device state to running.
> 
> Signed-off-by: zhengbin <zhengbin13@xxxxxxxxxx>
> ---
>  drivers/scsi/scsi_sysfs.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
> index 6a9040f..266e4c7 100644
> --- a/drivers/scsi/scsi_sysfs.c
> +++ b/drivers/scsi/scsi_sysfs.c
> @@ -772,6 +772,11 @@ store_state_field(struct device *dev, struct device_attribute *attr,
>  	mutex_lock(&sdev->state_mutex);
>  	ret = scsi_device_set_state(sdev, state);
>  	mutex_unlock(&sdev->state_mutex);
> +	/* If device state changes to SDEV_RUNNING, we need to run hw queue
> +	 * to avoid io hung.
> +	 */
> +	if (ret == 0 && state == SDEV_RUNNING)
> +		blk_mq_run_hw_queues(sdev->request_queue, true);
> 

Thinking of further, this way isn't safe, given the caller should make
sure that the queue is alive before calling blk_mq_run_hw_queues().

Now it is in sysfs write path, and the scsi device can become gone
just before calling blk_mq_run_hw_queues().


Thanks,
Ming



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