[PATCH v3 2/9] drm: hold master_lookup_lock when releasing a drm_file's master

[Desmond Cheong Zhi Xi]

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 at gmail.com>
---
 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