batman-adv: Convert batadv_softif_vlan to kref

batman-adv uses a self-written reference implementation which is just based
on atomic_t. This is less obvious when reading the code than kref and
therefore increases the change that the reference counting will be missed.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <a@unstable.cc>

net/batman-adv/soft-interface.c

@@ -30,6 +30,7 @@
 #include <linux/if_vlan.h>
 #include <linux/jiffies.h>
 #include <linux/kernel.h>
+#include <linux/kref.h>
 #include <linux/list.h>
 #include <linux/lockdep.h>
 #include <linux/netdevice.h>
@@ -477,9 +478,27 @@ out:
 	return;
 }
 
+/**
+ * batadv_softif_vlan_release - release vlan from lists and queue for free after
+ *  rcu grace period
+ * @ref: kref pointer of the vlan object
+ */
+static void batadv_softif_vlan_release(struct kref *ref)
+{
+	struct batadv_softif_vlan *vlan;
+
+	vlan = container_of(ref, struct batadv_softif_vlan, refcount);
+
+	spin_lock_bh(&vlan->bat_priv->softif_vlan_list_lock);
+	hlist_del_rcu(&vlan->list);
+	spin_unlock_bh(&vlan->bat_priv->softif_vlan_list_lock);
+
+	kfree_rcu(vlan, rcu);
+}
+
 /**
  * batadv_softif_vlan_free_ref - decrease the vlan object refcounter and
- *  possibly free it
+ *  possibly release it
  * @vlan: the vlan object to release
  */
 void batadv_softif_vlan_free_ref(struct batadv_softif_vlan *vlan)
@@ -487,13 +506,7 @@ void batadv_softif_vlan_free_ref(struct batadv_softif_vlan *vlan)
 	if (!vlan)
 		return;
 
-	if (atomic_dec_and_test(&vlan->refcount)) {
-		spin_lock_bh(&vlan->bat_priv->softif_vlan_list_lock);
-		hlist_del_rcu(&vlan->list);
-		spin_unlock_bh(&vlan->bat_priv->softif_vlan_list_lock);
-
-		kfree_rcu(vlan, rcu);
-	}
+	kref_put(&vlan->refcount, batadv_softif_vlan_release);
 }
 
 /**
@@ -514,7 +527,7 @@ struct batadv_softif_vlan *batadv_softif_vlan_get(struct batadv_priv *bat_priv,
 		if (vlan_tmp->vid != vid)
 			continue;
 
-		if (!atomic_inc_not_zero(&vlan_tmp->refcount))
+		if (!kref_get_unless_zero(&vlan_tmp->refcount))
 			continue;
 
 		vlan = vlan_tmp;
@@ -549,7 +562,7 @@ int batadv_softif_create_vlan(struct batadv_priv *bat_priv, unsigned short vid)
 
 	vlan->bat_priv = bat_priv;
 	vlan->vid = vid;
-	atomic_set(&vlan->refcount, 1);
+	kref_init(&vlan->refcount);
 
 	atomic_set(&vlan->ap_isolation, 0);