[Intel-gfx] [PATCH 1/9] drm/connector: Make the drm_sysfs connector->kdev device hold a reference to the connector

[Hans de Goede]

Userspace could hold open a reference to the connector->kdev device,
through e.g. holding a sysfs-atrtribute open after
drm_sysfs_connector_remove() has been called. In this case the connector
could be free-ed while the connector->kdev device's drvdata is still
pointing to it.

Give drm_connector devices there own device type, which allows
us to specify our own release function and make drm_sysfs_connector_add()
take a reference on the connector object, and have the new release
function put the reference when the device is released.

Giving drm_connector devices there own device type, will also allow
checking if a device is a drm_connector device with a
"if (device->type == &drm_sysfs_device_connector)" check.

Note that the setting of the name member of the device_type struct will
cause udev events for drm_connector-s to now contain DEVTYPE=drm_connector
as extra info. So this extends the uevent part of the userspace API.

Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/gpu/drm/drm_sysfs.c | 54 +++++++++++++++++++++++++++++++------
 1 file changed, 46 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/drm_sysfs.c b/drivers/gpu/drm/drm_sysfs.c
index f0336c804639..c344c6d5e738 100644
--- a/drivers/gpu/drm/drm_sysfs.c
+++ b/drivers/gpu/drm/drm_sysfs.c
@@ -50,6 +50,10 @@ static struct device_type drm_sysfs_device_minor = {
 	.name = "drm_minor"
 };
 
+static struct device_type drm_sysfs_device_connector = {
+	.name = "drm_connector",
+};
+
 struct class *drm_class;
 
 static char *drm_devnode(struct device *dev, umode_t *mode)
@@ -271,30 +275,64 @@ static const struct attribute_group *connector_dev_groups[] = {
 	NULL
 };
 
+static void drm_sysfs_connector_release(struct device *dev)
+{
+	struct drm_connector *connector = to_drm_connector(dev);
+
+	drm_connector_put(connector);
+	kfree(dev);
+}
+
 int drm_sysfs_connector_add(struct drm_connector *connector)
 {
 	struct drm_device *dev = connector->dev;
+	struct device *kdev;
+	int r;
 
 	if (connector->kdev)
 		return 0;
 
-	connector->kdev =
-		device_create_with_groups(drm_class, dev->primary->kdev, 0,
-					  connector, connector_dev_groups,
-					  "card%d-%s", dev->primary->index,
-					  connector->name);
+	kdev = kzalloc(sizeof(*kdev), GFP_KERNEL);
+	if (!kdev)
+		return -ENOMEM;
+
+	device_initialize(kdev);
+	kdev->class = drm_class;
+	kdev->type = &drm_sysfs_device_connector;
+	kdev->parent = dev->primary->kdev;
+	kdev->groups = connector_dev_groups;
+	kdev->release = drm_sysfs_connector_release;
+	dev_set_drvdata(kdev, connector);
+
+	r = dev_set_name(kdev, "card%d-%s", dev->primary->index, connector->name);
+	if (r)
+		goto err_free;
+
 	DRM_DEBUG("adding \"%s\" to sysfs\n",
 		  connector->name);
 
-	if (IS_ERR(connector->kdev)) {
-		DRM_ERROR("failed to register connector device: %ld\n", PTR_ERR(connector->kdev));
-		return PTR_ERR(connector->kdev);
+	r = device_add(kdev);
+	if (r) {
+		DRM_ERROR("failed to register connector device: %d\n", r);
+		goto err_free;
 	}
 
+	/*
+	 * Ensure the connector object does not get free-ed if userspace still has
+	 * references open to the device through e.g. the connector sysfs-attributes.
+	 */
+	drm_connector_get(connector);
+
+	connector->kdev = kdev;
+
 	if (connector->ddc)
 		return sysfs_create_link(&connector->kdev->kobj,
 				 &connector->ddc->dev.kobj, "ddc");
 	return 0;
+
+err_free:
+	put_device(kdev);
+	return r;
 }
 
 void drm_sysfs_connector_remove(struct drm_connector *connector)
-- 
2.31.1