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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: bee330f3d6 ("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
This commit is contained in:
Oleksandr Andrushchenko 2018-05-22 17:13:04 +03:00
parent fbecef1316
commit 069035c5db
1 changed files with 7 additions and 7 deletions
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14
drivers/gpu/drm/drm_drv.c
View File

@ -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);