drm/gem: handlecount isn't really a kref so don't make it one.

There were lots of places being inconsistent since handle count
looked like a kref but it really wasn't.

Fix this my just making handle count an atomic on the object,
and have it increase the normal object kref.

Now i915/radeon/nouveau drivers can drop the normal reference on
userspace object creation, and have the handle hold it.

This patch fixes a memory leak or corruption on unload, because
the driver had no way of knowing if a handle had been actually
added for this object, and the fbcon object needed to know this
to clean itself up properly.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 13 insertions, 5 deletions

diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index 774e1d49509b..07e4726a4ee0 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -612,7 +612,7 @@ struct drm_gem_object {
         struct kref refcount;
 
         /** Handle count of this object. Each handle also holds a reference */
-        struct kref handlecount;
+        atomic_t handle_count; /* number of handles on this object */
 
         /** Related drm device */
         struct drm_device *dev;
@@ -1461,7 +1461,7 @@ struct drm_gem_object *drm_gem_object_alloc(struct drm_device *dev,
                                             size_t size);
 int drm_gem_object_init(struct drm_device *dev,
                         struct drm_gem_object *obj, size_t size);
-void drm_gem_object_handle_free(struct kref *kref);
+void drm_gem_object_handle_free(struct drm_gem_object *obj);
 void drm_gem_vm_open(struct vm_area_struct *vma);
 void drm_gem_vm_close(struct vm_area_struct *vma);
 int drm_gem_mmap(struct file *filp, struct vm_area_struct *vma);
@@ -1496,7 +1496,7 @@ static inline void
 drm_gem_object_handle_reference(struct drm_gem_object *obj)
 {
         drm_gem_object_reference(obj);
-        kref_get(&obj->handlecount);
+        atomic_inc(&obj->handle_count);
 }
 
 static inline void
@@ -1505,12 +1505,15 @@ drm_gem_object_handle_unreference(struct drm_gem_object *obj)
         if (obj == NULL)
                 return;
 
+        if (atomic_read(&obj->handle_count) == 0)
+                return;
         /*
          * Must bump handle count first as this may be the last
          * ref, in which case the object would disappear before we
          * checked for a name
          */
-        kref_put(&obj->handlecount, drm_gem_object_handle_free);
+        if (atomic_dec_and_test(&obj->handle_count))
+                drm_gem_object_handle_free(obj);
         drm_gem_object_unreference(obj);
 }
 
@@ -1520,12 +1523,17 @@ drm_gem_object_handle_unreference_unlocked(struct drm_gem_object *obj)
         if (obj == NULL)
                 return;
 
+        if (atomic_read(&obj->handle_count) == 0)
+                return;
+
         /*
         * Must bump handle count first as this may be the last
         * ref, in which case the object would disappear before we
         * checked for a name
         */
-        kref_put(&obj->handlecount, drm_gem_object_handle_free);
+
+        if (atomic_dec_and_test(&obj->handle_count))
+                drm_gem_object_handle_free(obj);
         drm_gem_object_unreference_unlocked(obj);
 }