drm/radeon: fix rare segfault

In gem idle/busy ioctl the radeon object was derefenced after
drm_gem_object_unreference_unlocked which in case the object
have been destroyed lead to use of a possibly free pointer with
possibly wrong data.
Signed-off-by: Jerome Glisse <jglisse@redhat.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_gem.c

@@ -292,6 +292,7 @@ int radeon_gem_mmap_ioctl(struct drm_device *dev, void *data,
 int radeon_gem_busy_ioctl(struct drm_device *dev, void *data,
 			  struct drm_file *filp)
 {
+	struct radeon_device *rdev = dev->dev_private;
 	struct drm_radeon_gem_busy *args = data;
 	struct drm_gem_object *gobj;
 	struct radeon_bo *robj;
@@ -317,13 +318,14 @@ int radeon_gem_busy_ioctl(struct drm_device *dev, void *data,
 		break;
 	}
 	drm_gem_object_unreference_unlocked(gobj);
-	r = radeon_gem_handle_lockup(robj->rdev, r);
+	r = radeon_gem_handle_lockup(rdev, r);
 	return r;
 }
 
 int radeon_gem_wait_idle_ioctl(struct drm_device *dev, void *data,
 			      struct drm_file *filp)
 {
+	struct radeon_device *rdev = dev->dev_private;
 	struct drm_radeon_gem_wait_idle *args = data;
 	struct drm_gem_object *gobj;
 	struct radeon_bo *robj;
@@ -336,10 +338,10 @@ int radeon_gem_wait_idle_ioctl(struct drm_device *dev, void *data,
 	robj = gem_to_radeon_bo(gobj);
 	r = radeon_bo_wait(robj, NULL, false);
 	/* callback hw specific functions if any */
-	if (robj->rdev->asic->ioctl_wait_idle)
-		robj->rdev->asic->ioctl_wait_idle(robj->rdev, robj);
+	if (rdev->asic->ioctl_wait_idle)
+		robj->rdev->asic->ioctl_wait_idle(rdev, robj);
 	drm_gem_object_unreference_unlocked(gobj);
-	r = radeon_gem_handle_lockup(robj->rdev, r);
+	r = radeon_gem_handle_lockup(rdev, r);
 	return r;
 }