failover_add_primary() calls qdev_device_add() and doesn't unref
the device. Because of that, when the device is unplugged a reference
is remaining and prevents the cleanup of the object.

This prevents to be able to plugin back the failover primary device,
with errors like:

  (qemu) device_add vfio-pci,host=0000:41:00.0,id=hostdev0,bus=root.3,failover_pair_id=net0
  (qemu) device_del hostdev0

We can check with "info qtree" and "info pci" that the device has been removed, and then:

  (qemu) device_add vfio-pci,host=0000:41:00.0,id=hostdev1,bus=root.3,failover_pair_id=net0
  Error: vfio 0000:41:00.0: device is already attached
  (qemu) device_add vfio-pci,host=0000:41:00.0,id=hostdev0,bus=root.3,failover_pair_id=net0
  qemu-kvm: Duplicate ID 'hostdev0' for device

Fixes: 21e8709b29cd ("failover: Remove primary_dev member")
Cc: quintela@redhat.com
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 hw/net/virtio-net.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 5150f295e8c5..1c5af08dc556 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -862,6 +862,8 @@ static void failover_add_primary(VirtIONet *n, Error **errp)
         dev = qdev_device_add(opts, &err);
         if (err) {
             qemu_opts_del(opts);
+        } else {
+            object_unref(OBJECT(dev));
         }
     } else {
         error_setg(errp, "Primary device not found");
-- 
2.29.2

On Sat, Feb 06, 2021 at 01:39:55PM +0100, Laurent Vivier wrote:
>failover_add_primary() calls qdev_device_add() and doesn't unref
>the device. Because of that, when the device is unplugged a reference
>is remaining and prevents the cleanup of the object.
>
>This prevents to be able to plugin back the failover primary device,
>with errors like:
>
>  (qemu) device_add vfio-pci,host=0000:41:00.0,id=hostdev0,bus=root.3,failover_pair_id=net0
>  (qemu) device_del hostdev0
>
>We can check with "info qtree" and "info pci" that the device has been removed, and then:
>
>  (qemu) device_add vfio-pci,host=0000:41:00.0,id=hostdev1,bus=root.3,failover_pair_id=net0
>  Error: vfio 0000:41:00.0: device is already attached
>  (qemu) device_add vfio-pci,host=0000:41:00.0,id=hostdev0,bus=root.3,failover_pair_id=net0
>  qemu-kvm: Duplicate ID 'hostdev0' for device
>
>Fixes: 21e8709b29cd ("failover: Remove primary_dev member")
>Cc: quintela@redhat.com
>Signed-off-by: Laurent Vivier <lvivier@redhat.com>
>---
> hw/net/virtio-net.c | 2 ++
> 1 file changed, 2 insertions(+)
>

Reviewed-by: Jens Freimann <jfreimann@redhat.com>

Thank you Laurent!

regards,
Jens 

CC: Michael

On 06/02/2021 13:39, Laurent Vivier wrote:
> failover_add_primary() calls qdev_device_add() and doesn't unref
> the device. Because of that, when the device is unplugged a reference
> is remaining and prevents the cleanup of the object.
> 
> This prevents to be able to plugin back the failover primary device,
> with errors like:
> 
>   (qemu) device_add vfio-pci,host=0000:41:00.0,id=hostdev0,bus=root.3,failover_pair_id=net0
>   (qemu) device_del hostdev0
> 
> We can check with "info qtree" and "info pci" that the device has been removed, and then:
> 
>   (qemu) device_add vfio-pci,host=0000:41:00.0,id=hostdev1,bus=root.3,failover_pair_id=net0
>   Error: vfio 0000:41:00.0: device is already attached
>   (qemu) device_add vfio-pci,host=0000:41:00.0,id=hostdev0,bus=root.3,failover_pair_id=net0
>   qemu-kvm: Duplicate ID 'hostdev0' for device
> 
> Fixes: 21e8709b29cd ("failover: Remove primary_dev member")
> Cc: quintela@redhat.com
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
>  hw/net/virtio-net.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 5150f295e8c5..1c5af08dc556 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -862,6 +862,8 @@ static void failover_add_primary(VirtIONet *n, Error **errp)
>          dev = qdev_device_add(opts, &err);
>          if (err) {
>              qemu_opts_del(opts);
> +        } else {
> +            object_unref(OBJECT(dev));
>          }
>      } else {
>          error_setg(errp, "Primary device not found");
>