[PATCH 4/5] vfio: Use a refcount_t instead of a kref in the vfio_group

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The next patch adds a struct device to the struct vfio_group, and it is
confusing/bad practice to have two krefs in the same struct. This kref is
controlling the period when the vfio_group is registered in sysfs, and
visible in the internal lookup. Switch it to a refcount_t instead.

The refcount_dec_and_mutex_lock() is still required because we need
atomicity of the list searches and sysfs presence.

Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
---
 drivers/vfio/vfio.c | 19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index bf233943dc992f..dbe7edd88ce35c 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -69,7 +69,7 @@ struct vfio_unbound_dev {
 };
 
 struct vfio_group {
-	struct kref			kref;
+	refcount_t users;
 	int				minor;
 	atomic_t			container_users;
 	struct iommu_group		*iommu_group;
@@ -381,7 +381,7 @@ static struct vfio_group *vfio_create_group(struct iommu_group *iommu_group,
 	if (!group)
 		return ERR_PTR(-ENOMEM);
 
-	kref_init(&group->kref);
+	refcount_set(&group->users, 1);
 	INIT_LIST_HEAD(&group->device_list);
 	mutex_init(&group->device_lock);
 	INIT_LIST_HEAD(&group->unbound_list);
@@ -441,10 +441,10 @@ static struct vfio_group *vfio_create_group(struct iommu_group *iommu_group,
 	return group;
 }
 
-/* called with vfio.group_lock held */
-static void vfio_group_release(struct kref *kref)
+static void vfio_group_put(struct vfio_group *group)
 {
-	struct vfio_group *group = container_of(kref, struct vfio_group, kref);
+	if (!refcount_dec_and_mutex_lock(&group->users, &vfio.group_lock))
+		return;
 
 	WARN_ON(!list_empty(&group->device_list));
 	WARN_ON(atomic_read(&group->container_users));
@@ -456,15 +456,9 @@ static void vfio_group_release(struct kref *kref)
 	vfio_group_unlock_and_free(group);
 }
 
-static void vfio_group_put(struct vfio_group *group)
-{
-	kref_put_mutex(&group->kref, vfio_group_release, &vfio.group_lock);
-}
-
-/* Assume group_lock or group reference is held */
 static void vfio_group_get(struct vfio_group *group)
 {
-	kref_get(&group->kref);
+	refcount_inc(&group->users);
 }
 
 static struct vfio_group *vfio_group_get_from_minor(int minor)
@@ -1662,6 +1656,7 @@ struct vfio_group *vfio_group_get_external_user(struct file *filep)
 	if (ret)
 		return ERR_PTR(ret);
 
+	/* Since the caller holds the fget on the file users must be >= 1 */
 	vfio_group_get(group);
 
 	return group;
-- 
2.33.0




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