drm: Fix drm_release() and device unplug

This change “drm: Fix drm_release() and device unplug” (commit 3f04e0a) in Linux kernel is authored by Noralf Trønnes <noralf [at] tronnes.org> on Fri Feb 8 15:01:02 2019 +0100.

Description of "drm: Fix drm_release() and device unplug"

The change “drm: Fix drm_release() and device unplug” introduces changes as follows.

drm: Fix drm_release() and device unplug

If userspace has open fd(s) when drm_dev_unplug() is run, it will result
in drm_dev_unregister() being called twice. First in drm_dev_unplug() and
then later in drm_release() through the call to drm_put_dev().

Since userspace already holds a ref on drm_device through the drm_minor,
it's not necessary to add extra ref counting based on no open file
handles. Instead just drm_dev_put() unconditionally in drm_dev_unplug().

We now have this:
- Userpace holds a ref on drm_device as long as there's open fd(s)
- The driver holds a ref on drm_device as long as it's bound to the
  struct device

When both sides are done with drm_device, it is released.

Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Sean Paul <sean@poorly.run>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190208140103.28919-2-noralf@tronnes.org

Linux kernel releases containing commit 3f04e0a

The Linux kernel releases containing this commit are as follows.

Linux kernel code changes from "drm: Fix drm_release() and device unplug"

There are 12 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/gpu/drm/drm_drv.c  | 6 +-----
 drivers/gpu/drm/drm_file.c | 6 ++----
 2 files changed, 3 insertions(+), 9 deletions(-)
diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 381581b01d48..05bbc2b622fc 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -376,11 +376,7 @@ void drm_dev_unplug(struct drm_device *dev)
-	mutex_lock(&drm_global_mutex);
-	if (dev->open_count == 0)
-		drm_dev_put(dev);
-	mutex_unlock(&drm_global_mutex);
+	drm_dev_put(dev);
diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
index 83a5bbca6e7e..7caa3c7ed978 100644
--- a/drivers/gpu/drm/drm_file.c
+++ b/drivers/gpu/drm/drm_file.c
@@ -489,11 +489,9 @@ int drm_release(struct inode *inode, struct file *filp)
-	if (!--dev->open_count) {
+	if (!--dev->open_count)
-		if (drm_dev_is_unplugged(dev))
-			drm_put_dev(dev);
-	}

The commit for this change in Linux stable tree is 3f04e0a (patch).

Last modified: 2020/02/09