drm: remove minor-id during unplug

Don't delay minor removal to drm_put_minor(). Otherwise, user-space can
still open the minor and cause the kernel to oops. Instead, remove the
minor during unplug so any new open() will fail to access this minor.

Note that open() and drm_unplug_minor() are both protected by the global
DRM mutex so we're fine.
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_stub.c

@@ -346,6 +346,7 @@ static void drm_unplug_minor(struct drm_minor *minor)
 #endif
 
 	drm_sysfs_device_remove(minor);
+	idr_remove(&drm_minors_idr, minor->index);
 }
 
 /**
@@ -365,9 +366,6 @@ static void drm_put_minor(struct drm_minor *minor)
 	DRM_DEBUG("release secondary minor %d\n", minor->index);
 
 	drm_unplug_minor(minor);
-
-	idr_remove(&drm_minors_idr, minor->index);
-
 	kfree(minor);
 }