Re: [PATCH resubmit] xen-blkfront: Don't send closing notification to backend in blkfront_closing()

[Joe Jin <joe.jin@oracle.com>]

On 07/14/11 16:13, Ian Campbell wrote:
> On Wed, 2011-07-13 at 01:47 +0100, Joe Jin wrote:
>> When we do block device attach/detach test with below steps, umount hang and the
>> guest unable to shutdown:
>>
>> 1. start guest with the latest kernel.
>> 2. attach new block device by xm block-attach in Dom0
>> 3. mount new disk in guest
>> 4. execute xm block-detach to detach the block device in dom0 until timeout
>> 5. try to unmount the disk in guest, umount hung. at here, any IOs to the 
>>    device will hang.
>>
>> Checking the code found when 'xm block-detach' set backend device's state to
>> 'XenbusStateClosing', frontend received the notification and blkfront_closing()
>> be called, at the moment, the disk still using by guest, so frontend refused
>> to close. In the blkfront_closing(), frontend send a notification to backend
>> said that the its state switched to 'Closing', when backend got the
>> event, it will disconnect from real device, at here any IO request will
>> be stuck, even tried to release the disk by umount.
>>
>> Per our test, below patch fix this issue.
> 
> It's worth mentioning here that the change to xbdev->state is picked up
> in blkif_release() when the device is closed and the disconnect happens
> at that point instead.

This is right, thanks for the suggestions.

> 
> I'm wondering if we might not be better off deferring the disconnect on
> the backend side until the frontend enters XenbusStateClosed instead of
> doing it in closing.

Yes this fix from backend side works too, also this looks reasonable than 
fix in frontend.

Konrad, any advice?

Thanks,
Joe

> 
> Ian
> 
>>
>> Signed-off-by: Joe Jin <joe.jin@oracle.com>
>> Signed-off-by: Annie Li <annie.li@oracle.com>
>> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>> Cc: Jens Axboe <jaxboe@fusionio.com>
>> Cc: stable@kernel.org
>>
>> ---
>>  xen-blkfront.c |    2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
>> index b536a9c..f6d8ac2 100644
>> --- a/drivers/block/xen-blkfront.c
>> +++ b/drivers/block/xen-blkfront.c
>> @@ -1088,7 +1088,7 @@ blkfront_closing(struct blkfront_info *info)
>>  	if (bdev->bd_openers) {
>>  		xenbus_dev_error(xbdev, -EBUSY,
>>  				 "Device in use; refusing to close");
>> -		xenbus_switch_state(xbdev, XenbusStateClosing);
>> +		xbdev->state = XenbusStateClosing;
>>  	} else {
>>  		xlvbd_release_gendisk(info);
>>  		xenbus_frontend_closed(xbdev);
> 
> 


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