VFIO fixes for v4.11-rc4

- Rework sanity check for mdev driver group notifier de-registration
    (Alex Williamson)
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Merge tag 'vfio-v4.11-rc4' of git://github.com/awilliam/linux-vfio

Pull VFIO fix from Alex Williamson:
 "Rework sanity check for mdev driver group notifier de-registration
  (Alex Williamson)"

* tag 'vfio-v4.11-rc4' of git://github.com/awilliam/linux-vfio:
  vfio: Rework group release notifier warning

drivers/vfio/vfio.c

@@ -403,6 +403,7 @@ static void vfio_group_release(struct kref *kref)
 	struct iommu_group *iommu_group = group->iommu_group;
 
 	WARN_ON(!list_empty(&group->device_list));
+	WARN_ON(group->notifier.head);
 
 	list_for_each_entry_safe(unbound, tmp,
 				 &group->unbound_list, unbound_next) {
@@ -1573,6 +1574,10 @@ static int vfio_group_fops_open(struct inode *inode, struct file *filep)
 		return -EBUSY;
 	}
 
+	/* Warn if previous user didn't cleanup and re-init to drop them */
+	if (WARN_ON(group->notifier.head))
+		BLOCKING_INIT_NOTIFIER_HEAD(&group->notifier);
+
 	filep->private_data = group;
 
 	return 0;
@@ -1584,9 +1589,6 @@ static int vfio_group_fops_release(struct inode *inode, struct file *filep)
 
 	filep->private_data = NULL;
 
-	/* Any user didn't unregister? */
-	WARN_ON(group->notifier.head);
-
 	vfio_group_try_dissolve_container(group);
 
 	atomic_dec(&group->opened);