drm: Set final_kfree in drm_dev_alloc

I also did a full review of all callers, and only the xen driver
forgot to call drm_dev_put in the failure path. Fix that up too.

v2: I noticed that xen has a drm_driver.release hook, and uses
drm_dev_alloc(). We need to remove the kfree from
xen_drm_drv_release().

bochs also has a release hook, but leaked the drm_device ever since

commit 0a6659bd
Author: Gerd Hoffmann <kraxel@redhat.com>
Date:   Tue Dec 17 18:04:46 2013 +0100

    drm/bochs: new driver

This patch here fixes that leak.

Same for virtio, started leaking with

commit b1df3a2b
Author: Gerd Hoffmann <kraxel@redhat.com>
Date:   Tue Feb 11 14:58:04 2020 +0100

    drm/virtio: add drm_driver.release callback.
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Cc: xen-devel@lists.xenproject.org
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Cc: xen-devel@lists.xenproject.org
Link: https://patchwork.freedesktop.org/patch/msgid/20200323144950.3018436-5-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_drv.c

@@ -39,6 +39,7 @@
 #include <drm/drm_color_mgmt.h>
 #include <drm/drm_drv.h>
 #include <drm/drm_file.h>
+#include <drm/drm_managed.h>
 #include <drm/drm_mode_object.h>
 #include <drm/drm_print.h>
 
@@ -819,6 +820,8 @@ struct drm_device *drm_dev_alloc(struct drm_driver *driver,
 		return ERR_PTR(ret);
 	}
 
+	drmm_add_final_kfree(dev, dev);
+
 	return dev;
 }
 EXPORT_SYMBOL(drm_dev_alloc);

drivers/gpu/drm/xen/xen_drm_front.c

@@ -461,7 +461,6 @@ static void xen_drm_drv_release(struct drm_device *dev)
 	drm_mode_config_cleanup(dev);
 
 	drm_dev_fini(dev);
-	kfree(dev);
 
 	if (front_info->cfg.be_alloc)
 		xenbus_switch_state(front_info->xb_dev,
@@ -561,6 +560,7 @@ static int xen_drm_drv_init(struct xen_drm_front_info *front_info)
 fail_modeset:
 	drm_kms_helper_poll_fini(drm_dev);
 	drm_mode_config_cleanup(drm_dev);
+	drm_dev_put(drm_dev);
 fail:
 	kfree(drm_info);
 	return ret;