On 2011年08月04日 05:49, Konrad Rzeszutek Wilk wrote:
> On Wed, Aug 03, 2011 at 02:03:14PM +0800, Joe Jin wrote:
>> This patchset is a backport and original patch author is Daniel Stodden:
>> http://xenbits.xen.org/hg/XCP/linux-2.6.32.pq.hg/file/tip/CA-7672-blkback-shutdown.patch
>>
>> Initial issue:
>> When we do block device attach/detach test with below steps, umount hang
>> in guest and the guest unable to shutdown:
>
> So the patchset looks good and it fixes the guest hanging.. but
>>
>> 1. start guest with the latest kernel.
>> 2. attach new block device by xm block-attach in Dom0
>
> So I think your patch while it fixes this problem it introduces a bug:
>
> I did this in Dom0:
>
> 18:10:23 # 5 :~/
>> xm block-attach 1 phy:/dev/sda xvda w
>
> and did _not_ attach the disk in the guest. Then I did
>
>
> 18:10:35 # 6 :~/
>> xm block-list 1
> Vdev BE handle state evt-ch ring-ref BE-path
> 51712 0 0 4 18 770 /local/domain/0/backend/vbd/1/51712
>
> 18:10:39 # 7 :~/
>> xm block-detach 1 51712
>
> 18:10:46 # 8 :~/
>> xm block-list 1
>
>
>
> If I try the same sequence of events with your patch, I get this:
>
> 1:28:06 # 1 :~/
>> xm list
> Name ID Mem VCPUs State
> Time(s)
> Domain-0 0 1500 4 r----- 1246.6
> sda 2 2048 2 -b---- 1034.7
> sdb 6 2048 2 -b---- 3.4
> 21:28:09 # 2 :~/
>> xm block-list 6
>
> 21:28:22 # 4 :~/
>> xm block-attach 6 phy:/dev/sdb xvda w
>
> [did not do anything in the guest]
> 21:28:33 # 5 :~/
>> xm block-list 6
> Vdev BE handle state evt-ch ring-ref BE-path
> 51712 0 0 4 18 770 /local/domain/0/backend/vbd/6/51712
>
> 21:28:37 # 6 :~/
>> xm block-detach 6 51712
> Error: Device 51712 (vbd) could not be disconnected.
> Usage: xm block-detach <Domain> <DevId> [-f|--force]
>
> Destroy a domain's virtual block device.
>
> 21:30:30 # 7 :~/
>
> Any ideas?
Konrad,
Thanks for the finding.
Review the patch looked like it caused by below piece of codes in patch3:
case XenbusStateClosed:
- xenbus_switch_state(dev, XenbusStateClosed);
- if (xenbus_dev_is_online(dev))
- break;
- /* fall through if not online */
+ if (!xenvbd_kthread_remove(be))
+ xenvbd_signal_shutdown(be);
+ break;
+
case XenbusStateUnknown:
- /* implies blkif_disconnect() via blkback_remove() */
+ /* implies xen_blkif_disconnect() via blkback_remove() */
device_unregister(&dev->dev);
break;
When device's state switched to XenbusStateClosed, did not unregister the
device.
Will send new patches for this.
Regards,
Joe
>> 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.
>>
>> Root cause:
>> This caused by 'xm block-detach' in Dom0 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.
>>
>> So this may fix either frontend or backend, I have send a fix for frontend:
>> https://lkml.org/lkml/2011/7/8/159
>> Ian think we should fix it from backend and he pointed out Daniel Stodden
>> have
>> submitted a patch(see above link) for xen-blkback, I tried it and it works
>> well.
>>
>> Changes:
>> v2:
>> - Reformat code style.
>> - Per Knoard suggestions, change some int defines to bool.
>>
>> drivers/block/xen-blkback/blkback.c | 10 +--
>> drivers/block/xen-blkback/common.h | 5 +
>> drivers/block/xen-blkback/xenbus.c | 203
>> +++++++++++++++++++++++++++++++++++++++++++++++++++++++-------
>> 3 files changed, 192 insertions(+), 26 deletions(-)
--
Oracle <http://www.oracle.com>
Joe Jin | Team Leader, Software Development | +8610.6106.5624
ORACLE | Linux and Virtualization
No. 24 Zhongguancun Software Park, Haidian District | 100193 Beijing
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