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[Xen-devel] Re: xen-blkfront: Don't send closing notification to backend

To: Joe Jin <joe.jin@xxxxxxxxxx>
Subject: [Xen-devel] Re: xen-blkfront: Don't send closing notification to backend in blkfront_closing()
From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Date: Fri, 8 Jul 2011 12:04:14 -0400
Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, Ian Campbell <ian.campbell@xxxxxxxxxx>, Kurt C Hackel <KURT.HACKEL@xxxxxxxxxx>, Greg Marsden <greg.marsden@xxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, annie.li@xxxxxxxxxx, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Jens Axboe <jaxboe@xxxxxxxxxxxx>, Daniel Stodden <daniel.stodden@xxxxxxxxxx>
Delivery-date: Fri, 08 Jul 2011 09:05:26 -0700
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On Fri, Jul 08, 2011 at 03:14:29PM +0800, Joe Jin wrote:
> When we do block attach detach test with below steps, umount hang and the
> guest unable to shutdown:
> 1. start guest with the latest kernel.
> 2. attach new disk by xm-attach in Dom0
> 3. mount new disk in guest
> 4. detach the disk by xm-detach in dom0

I think you mean xm block-detach and xm-attach?

I tried with and without your patch and in both cases I get
this in my guest:

sh-4.1# mount /dev/xvda /test
[  385.949749] EXT3-fs: barriers not enabled
[  385.960173] kjournald starting.  Commit interval 5 seconds
[  385.960418] EXT3-fs (xvda): using internal journal
[  385.960427] EXT3-fs (xvda): mounted filesystem with writeback data mode
sh-4.1# [  411.176887] vbd vbd-51712: 16 Device in use; refusing to close

The commands on the other side (Dom0) were:

[root@tst009 ~]# xm block-list 6
Vdev  BE handle state evt-ch ring-ref BE-path
51712  0    0     4      12     770   /local/domain/0/backend/vbd/6/51712
[root@tst009 ~]# 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.
[root@tst009 ~]# xm block-detach 6 51712 -f

> 5. umount the partition/disk in guest, command hung. exactly at here, any
>    IO request to the partition/disk will hang.

I get that with the patch and without it:

sh-4.1# [  519.814048] block xvda: device/vbd/51712 was hot-unplugged, 1 stale 

sh-4.1# df -h
Filesystem            Size  Used Avail Use% Mounted on
none                  490M  120K  490M   1% /dev
none                  490M  131M  359M  27% 
shm                    10M     0   10M   0% /dev/shm
var_tmp                10M     0   10M   0% /var/tmp
/dev/xvda              20G  173M   19G   1% /test
sh-4.1# umount /test

Any ideas?
> Checking the code we found when xm-detach command set backend state to 
> Closing, will trigger blkback_changed() -> blkfront_closing() call.
> At the moment, the disk still opened by guest, so frontend will refuse the 
> request, but in the blkfront_closing(), it send a notification to backend 
> said that the frontend 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.
> Signed-off-by: Joe Jin <joe.jin@xxxxxxxxxx>
> Signed-off-by: Annie Li <annie.li@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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