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?
> 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(-)
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