vfio: fix noiommu vfio_iommu_group_get reference count

In vfio_iommu_group_get() we want to increase the reference count of the iommu group.

In noiommu case, the group does not exist and is allocated. iommu_group_add_device() increases the group ref count. However we then call iommu_group_put() which decrements it.

This leads to a "refcount_t: underflow WARN_ON".

---
 drivers/vfio/vfio.c | 1 -
 1 file changed, 1 deletion(-)

index 330d505..fd8d691 100644
@@ -138,7 +138,6 @@ struct iommu_group *vfio_iommu_group_get(struct device *dev)
 	iommu_group_set_name(group, "vfio-noiommu");
 	iommu_group_set_iommudata(group, &noiommu, NULL);
 	ret = iommu_group_add_device(group, dev);
-	iommu_group_put(group);
 	if (ret)
 		return NULL;
 

2.5.5

Yep, the group is created with an initial reference count of 1, we then add the device, which increments the reference count. Normally the instantiator of the group would then release the reference, so that only the device reference holds the group. However here we want a reference in addition to the device reference, so we should never have released the initial reference. Seems right, except...