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[Xen-devel] Re: [PATCH resubmit] xen-blkfront: Don't send closing notifi

To: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH resubmit] xen-blkfront: Don't send closing notification to backend in blkfront_closing()
From: Joe Jin <joe.jin@xxxxxxxxxx>
Date: Thu, 14 Jul 2011 16:55:05 +0800
Cc: Jeremy Fitzhardinge <Jeremy.Fitzhardinge@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, Kurt C Hackel <KURT.HACKEL@xxxxxxxxxx>, Greg Marsden <greg.marsden@xxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, "annie.li@xxxxxxxxxx" <annie.li@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Jens Axboe <jaxboe@xxxxxxxxxxxx>, "stable@xxxxxxxxxx" <stable@xxxxxxxxxx>, Daniel Stodden <Daniel.Stodden@xxxxxxxxxx>
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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?


> Ian
>> Signed-off-by: Joe Jin <joe.jin@xxxxxxxxxx>
>> Signed-off-by: Annie Li <annie.li@xxxxxxxxxx>
>> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
>> Cc: Jens Axboe <jaxboe@xxxxxxxxxxxx>
>> Cc: stable@xxxxxxxxxx
>> ---
>>  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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