drm: Extract drm_master_open

And pull out the primary_client check to make it really obvious that
this can't happen on control/render nodes. Bonus that we can avoid the
master lock in this case.

v2: Don't leak locks on error path (and simplify control flow while
at it), reported by Julia.

Cc: Julia Lawall <julia.lawall@lip6.fr>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1465930269-7883-6-git-send-email-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_auth.c

@@ -120,7 +120,7 @@ static struct drm_master *drm_master_create(struct drm_device *dev)
  * This function must be called with dev::struct_mutex held.
  * Returns negative error code on failure. Zero on success.
  */
-int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv)
+static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv)
 {
 	struct drm_master *old_master;
 	int ret;
@@ -226,6 +226,23 @@ out_unlock:
 	return ret;
 }
 
+int drm_master_open(struct drm_file *file_priv)
+{
+	struct drm_device *dev = file_priv->minor->dev;
+	int ret = 0;
+
+	/* if there is no current master make this fd it, but do not create
+	 * any master object for render clients */
+	mutex_lock(&dev->master_mutex);
+	if (!file_priv->minor->master)
+		ret = drm_new_set_master(dev, file_priv);
+	else
+		file_priv->master = drm_master_get(file_priv->minor->master);
+	mutex_unlock(&dev->master_mutex);
+
+	return ret;
+}
+
 struct drm_master *drm_master_get(struct drm_master *master)
 {
 	kref_get(&master->refcount);

drivers/gpu/drm/drm_fops.c

@@ -229,19 +229,11 @@ static int drm_open_helper(struct file *filp, struct drm_minor *minor)
 			goto out_prime_destroy;
 	}
 
-	/* if there is no current master make this fd it, but do not create
-	 * any master object for render clients */
-	mutex_lock(&dev->master_mutex);
-	if (drm_is_primary_client(priv) && !priv->minor->master) {
-		/* create a new master */
-		ret = drm_new_set_master(dev, priv);
+	if (drm_is_primary_client(priv)) {
+		ret = drm_master_open(priv);
 		if (ret)
 			goto out_close;
-	} else if (drm_is_primary_client(priv)) {
-		/* get a reference to the master */
-		priv->master = drm_master_get(priv->minor->master);
 	}
-	mutex_unlock(&dev->master_mutex);
 
 	mutex_lock(&dev->filelist_mutex);
 	list_add(&priv->lhead, &dev->filelist);
@@ -270,7 +262,6 @@ static int drm_open_helper(struct file *filp, struct drm_minor *minor)
 	return 0;
 
 out_close:
-	mutex_unlock(&dev->master_mutex);
 	if (dev->driver->postclose)
 		dev->driver->postclose(dev, priv);
 out_prime_destroy:

drivers/gpu/drm/drm_internal.h

@@ -66,7 +66,7 @@ int drm_setmaster_ioctl(struct drm_device *dev, void *data,
 			struct drm_file *file_priv);
 int drm_dropmaster_ioctl(struct drm_device *dev, void *data,
 			 struct drm_file *file_priv);
-int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv);
+int drm_master_open(struct drm_file *file_priv);
 
 /* drm_sysfs.c */
 extern struct class *drm_class;