Commit 069035c5 authored May 22, 2018 by Oleksandr Andrushchenko

drm: Fix possible race conditions while unplugging DRM device



When unplugging a hotpluggable DRM device we first unregister it
with drm_dev_unregister and then set drm_device.unplugged flag which
is used to mark device critical sections with drm_dev_enter()/
drm_dev_exit() preventing access to device resources that are not
available after the device is gone.
But drm_dev_unregister may lead to hotplug uevent(s) fired to
user-space on card and/or connector removal, thus making it possible
for user-space to try accessing a disconnected device.

Fix this by first making sure device is properly marked as
disconnected and only then unregister it.

Fixes: bee330f3 ("drm: Use srcu to protect drm_device.unplugged")

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Reported-by: Andrii Chepurnyi <andrii_chepurnyi@epam.com>
Cc: "Noralf Trønnes" <noralf@tronnes.org>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180522141304.18646-1-andr2000@gmail.com

parent fbecef13

drivers/gpu/drm/drm_drv.c

+7 −7

Original line number	Diff line number	Diff line
		@@ -369,13 +369,6 @@ EXPORT_SYMBOL(drm_dev_exit);
		*/
		void drm_dev_unplug(struct drm_device *dev)
		{
		drm_dev_unregister(dev);

		mutex_lock(&drm_global_mutex);
		if (dev->open_count == 0)
		drm_dev_put(dev);
		mutex_unlock(&drm_global_mutex);

		/*
		* After synchronizing any critical read section is guaranteed to see
		* the new value of ->unplugged, and any critical section which might
		@@ -384,6 +377,13 @@ void drm_dev_unplug(struct drm_device *dev)
		*/
		dev->unplugged = true;
		synchronize_srcu(&drm_unplug_srcu);

		drm_dev_unregister(dev);

		mutex_lock(&drm_global_mutex);
		if (dev->open_count == 0)
		drm_dev_put(dev);
		mutex_unlock(&drm_global_mutex);
		}
		EXPORT_SYMBOL(drm_dev_unplug);

Admin message