linux-kernel - Re: [PATCH 2/6] xen-blkfront: handle backend CLOSED without CLOSING

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Date:	Mon, 1 Oct 2012 18:19:19 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	David Vrabel <david.vrabel@...rix.com>
CC:	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/6] xen-blkfront: handle backend CLOSED without CLOSING

On 25/09/12 18:53, David Vrabel wrote:
> On 21/09/12 17:04, David Vrabel wrote:
>> From: David Vrabel <david.vrabel@...rix.com>
>>
>> Backend drivers shouldn't transistion to CLOSED unless the frontend is
>> CLOSED.  If a backend does transition to CLOSED too soon then the
>> frontend may not see the CLOSING state and will not properly shutdown.
>>
>> So, treat an unexpected backend CLOSED state the same as CLOSING.
> 
> Didn't handle the frontend block device being mounted. Updated patch here.

Konrad, can you ack this updated patch if you're happy with it.

Thanks.

David

> 8<---------------------------------
> xen-blkfront: handle backend CLOSED without CLOSING
> 
> Backend drivers shouldn't transistion to CLOSED unless the frontend is
> CLOSED.  If a backend does transition to CLOSED too soon then the
> frontend may not see the CLOSING state and will not properly shutdown.
> 
> So, treat an unexpected backend CLOSED state the same as CLOSING.
> 
> If the backend is CLOSED then the frontend can't talk to it so go to
> CLOSED immediately without waiting for the block device to be closed
> or unmounted.
> 
> Signed-off-by: David Vrabel <david.vrabel@...rix.com>
> ---
>  drivers/block/xen-blkfront.c |   13 +++++++++----
>  1 files changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index 2c2d2e5..c1f5f38 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -1143,7 +1143,8 @@ static int blkfront_resume(struct xenbus_device *dev)
>  }
>  
>  static void
> -blkfront_closing(struct blkfront_info *info)
> +blkfront_closing(struct blkfront_info *info,
> +		 enum xenbus_state backend_state)
>  {
>  	struct xenbus_device *xbdev = info->xbdev;
>  	struct block_device *bdev = NULL;
> @@ -1167,7 +1168,8 @@ blkfront_closing(struct blkfront_info *info)
>  
>  	mutex_lock(&bdev->bd_mutex);
>  
> -	if (bdev->bd_openers) {
> +	/* If the backend is already CLOSED, close now. */
> +	if (bdev->bd_openers && backend_state != XenbusStateClosed) {
>  		xenbus_dev_error(xbdev, -EBUSY,
>  				 "Device in use; refusing to close");
>  		xenbus_switch_state(xbdev, XenbusStateClosing);
> @@ -1340,15 +1342,18 @@ static void blkback_changed(struct xenbus_device *dev,
>  	case XenbusStateReconfiguring:
>  	case XenbusStateReconfigured:
>  	case XenbusStateUnknown:
> -	case XenbusStateClosed:
>  		break;
>  
>  	case XenbusStateConnected:
>  		blkfront_connect(info);
>  		break;
>  
> +	case XenbusStateClosed:
> +		if (dev->state == XenbusStateClosed)
> +			break;
> +		/* Missed the backend's Closing state -- fallthrough */
>  	case XenbusStateClosing:
> -		blkfront_closing(info);
> +		blkfront_closing(info, backend_state);
>  		break;
>  	}
>  }
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