Patch "drm: Don't race connector registration" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

drm: Don't race connector registration

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
drm-don-t-race-connector-registration.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Daniel Vetter <[email protected]>
Date: Thu, 12 Jan 2017 17:15:56 +0100
Subject: drm: Don't race connector registration

From: Daniel Vetter <[email protected]>

[ Upstream commit e6e7b48b295afa5a5ab440de0a94d9ad8b3ce2d0 ]

I was under the misconception that the sysfs dev stuff can be fully set up, and then registered all in one step with device_add. That's true for properties and property groups, but not for parents and child devices. Those must be fully registered before you can register a child.

Add a bit of tracking to make sure that asynchronous mst connector hotplugging gets this right. For consistency we rely upon the implicit barriers of the connector->mutex, which is taken anyway, to ensure that at least either the connector or device registration call will work out.

Mildly tested since I can't reliably reproduce this on my mst box here.

---
 drivers/gpu/drm/drm_connector.c |    3 +++
 drivers/gpu/drm/drm_drv.c       |    4 ++++
 include/drm/drmP.h              |    1 +
 3 files changed, 8 insertions(+)

@@ -379,6 +379,9 @@ int drm_connector_register(struct drm_co
 {
 	int ret = 0;
 
+	if (!connector->dev->registered)
+		return 0;
+
 	mutex_lock(&connector->mutex);
 	if (connector->registered)
 		goto unlock;

@@ -710,6 +710,8 @@ int drm_dev_register(struct drm_device *
 	if (ret)
 		goto err_minors;
 
+	dev->registered = true;
+
 	if (dev->driver->load) {
 		ret = dev->driver->load(dev, flags);
 		if (ret)

@@ -749,6 +751,8 @@ void drm_dev_unregister(struct drm_devic
 
 	drm_lastclose(dev);
 
+	dev->registered = false;
+
 	if (drm_core_check_feature(dev, DRIVER_MODESET))
 		drm_modeset_unregister_all(dev);
 

@@ -776,6 +776,7 @@ struct drm_device {
 	struct drm_minor *control;		/**< Control node */
 	struct drm_minor *primary;		/**< Primary node */
 	struct drm_minor *render;		/**< Render node */
+	bool registered;
 
 	/* currently active master for this device. Protected by master_mutex */
 	struct drm_master *master;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/drm-prevent-double-un-registration-for-connectors.patch queue-4.9/drm-don-t-race-connector-registration.patch