Re: [Xen-users] Xen shutdown fails to release DRBD device

[Valentin Vidic <Valentin.Vidic@xxxxxxxxx>]

On Wed, Aug 22, 2018 at 03:55:46PM +0200, Valentin Vidic wrote:
> DRBD end for this seems rather simple, it only checks if the
> device->open_cnt is zero. So it would seem like drbd_release
> was not called yet when the block-drbd script is run?
> 
> 
> static enum drbd_state_rv
> is_valid_state(struct drbd_device *device, union drbd_state ns)
> {
> ...
>         else if (ns.role == R_SECONDARY && device->open_cnt)
>                 rv = SS_DEVICE_IN_USE;
> ...
> }
> 
> static void drbd_release(struct gendisk *gd, fmode_t mode)
> {
>         struct drbd_device *device = gd->private_data;
>         mutex_lock(&drbd_main_mutex);
>         device->open_cnt--;
>         mutex_unlock(&drbd_main_mutex);
> }

On the Xen side it seems that XenbusStateClosed event is sent
to xenbus to run the block-drbd script.  However the call to
xen_blkif_disconnect in the line before that can fail with -EBUSY
if there is still some in-flight IO for the device.  Could it be
that a lot of IO during shutdown is holding the DRBD device open
while the block-drbd script has already started running?

/*
 * Callback received when the frontend's state changes.
 */
static void frontend_changed(struct xenbus_device *dev,
                             enum xenbus_state frontend_state)
{
...
        case XenbusStateClosed:
                xen_blkif_disconnect(be->blkif);
                xenbus_switch_state(dev, XenbusStateClosed);
                if (xenbus_dev_is_online(dev))
                        break;
                /* fall through if not online */
...
}

Maybe the XenbusStateClosed event should only be send when the
device is closed in xen_blkif_free or some other place?

-- 
Valentin

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