If we fail to hotplug virtio-blk device and then suspend
or shutdown VM, qemu is likely to crash.

Re-production steps:
1. Run VM named vm001
2. Create a virtio-blk.xml which contains wrong configurations:
<disk device="lun" rawio="yes" type="block">
  <driver cache="none" io="native" name="qemu" type="raw" />
  <source dev="/dev/mapper/11-dm" />
  <target bus="virtio" dev="vdx" />
</disk>
3. Run command : virsh attach-device vm001 virtio-blk.xml
error: Failed to attach device from blk-scsi.xml
error: internal error: unable to execute QEMU command 'device_add': Please set scsi=off for virtio-blk devices in order to use virtio 1.0
it means hotplug virtio-blk device failed.
4. Suspend or shutdown VM will leads to qemu crash

Problem happens in virtio_vmstate_change which is called by
vm_state_notify:
vdev’s parent_bus is NULL, so qdev_get_parent_bus(DEVICE(vdev)) will crash.
virtio_vmstate_change is added to the list vm_change_state_head at virtio_blk_device_realize(virtio_init),
but after hotplug virtio-blk failed, virtio_vmstate_change will not be removed from vm_change_state_head.
Adding unrealize function of virtio-blk device can solve this problem.

Signed-off-by: linzhecheng <linzhecheng@huawei.com>
---
 hw/virtio/virtio.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 5884ce3480..ea532dc35f 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -2491,6 +2491,7 @@ static void virtio_device_realize(DeviceState *dev, Error **errp)
     virtio_bus_device_plugged(vdev, &err);
     if (err != NULL) {
         error_propagate(errp, err);
+        vdc->unrealize(dev, NULL);
         return;
     }
 
-- 
2.12.2.windows.2

On Tue, Oct 31, 2017 at 04:03:03PM +0800, linzhecheng wrote:
> If we fail to hotplug virtio-blk device and then suspend
> or shutdown VM, qemu is likely to crash.
> 
> Re-production steps:
> 1. Run VM named vm001
> 2. Create a virtio-blk.xml which contains wrong configurations:
> <disk device="lun" rawio="yes" type="block">
>   <driver cache="none" io="native" name="qemu" type="raw" />
>   <source dev="/dev/mapper/11-dm" />
>   <target bus="virtio" dev="vdx" />
> </disk>
> 3. Run command : virsh attach-device vm001 virtio-blk.xml
> error: Failed to attach device from blk-scsi.xml
> error: internal error: unable to execute QEMU command 'device_add': Please set scsi=off for virtio-blk devices in order to use virtio 1.0
> it means hotplug virtio-blk device failed.
> 4. Suspend or shutdown VM will leads to qemu crash
> 
> Problem happens in virtio_vmstate_change which is called by
> vm_state_notify:
> vdev’s parent_bus is NULL, so qdev_get_parent_bus(DEVICE(vdev)) will crash.
> virtio_vmstate_change is added to the list vm_change_state_head at virtio_blk_device_realize(virtio_init),
> but after hotplug virtio-blk failed, virtio_vmstate_change will not be removed from vm_change_state_head.
> Adding unrealize function of virtio-blk device can solve this problem.
> 
> Signed-off-by: linzhecheng <linzhecheng@huawei.com>
> ---
>  hw/virtio/virtio.c | 1 +
>  1 file changed, 1 insertion(+)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>