[PATCH v2] vfio: fix noiommu vfio_iommu_group_get reference count

[Eric Auger]

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".

Only decrement the ref count in case of iommu_group_add_device
failure.

Signed-off-by: Eric Auger <eric.au...@redhat.com>

---

v1 -> v2:
put the group in case iommu_group_add_device failed
---
 drivers/vfio/vfio.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 330d505..4ee4f36 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -138,9 +138,10 @@ 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)
+       if (ret) {
+               iommu_group_put(group);
                return NULL;
+       }
 
        /*
         * Where to taint?  At this point we've added an IOMMU group for a
-- 
2.5.5