On Wed, Aug 18, 2021 at 03:38:17PM +0800, Desmond Cheong Zhi Xi wrote:

When drm_file.master changes value, the corresponding drm_device.master_lookup_lock should be held.

In drm_master_release, a call to drm_master_put sets the file_priv->master to NULL, so we protect this section with drm_device.master_lookup_lock.

Signed-off-by: Desmond Cheong Zhi Xi desmondcheongzx@gmail.com

At this points all refcounts to drm_file have disappeared, so yeah this is a lockless access, but also no one can observe it anymore. See also next patch.

Hence I think the current code is fine. -Daniel

---

drivers/gpu/drm/drm_auth.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c index 8efb58aa7d95..8c0e0dba1611 100644 --- a/drivers/gpu/drm/drm_auth.c +++ b/drivers/gpu/drm/drm_auth.c @@ -373,8 +373,11 @@ void drm_master_release(struct drm_file *file_priv) } /* drop the master reference held by the file priv */

• if (file_priv->master)

• if (file_priv->master) {

• spin_lock(&dev->master_lookup_lock);
  

  drm_master_put(&file_priv->master);

• spin_unlock(&dev->master_lookup_lock);
  

• } mutex_unlock(&dev->master_mutex);

} -- 2.25.1