batman-adv: postpone sysfs removal when unregistering

When processing the unregister notify for a hard interface, removing
the sysfs files may lead to a circular deadlock (rtnl mutex <->
s_active).

To overcome this problem, postpone the sysfs removal in a worker.

Reported-by: Sasha Levin <sasha.levin@oracle.com>
Reported-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>
Signed-off-by: Antonio Quartulli <ordex@autistici.org>

net/batman-adv/hard-interface.c

@@ -457,6 +457,24 @@ void batadv_hardif_disable_interface(struct batadv_hard_iface *hard_iface)
 		batadv_hardif_free_ref(primary_if);
 }
 
+/**
+ * batadv_hardif_remove_interface_finish - cleans up the remains of a hardif
+ * @work: work queue item
+ *
+ * Free the parts of the hard interface which can not be removed under
+ * rtnl lock (to prevent deadlock situations).
+ */
+static void batadv_hardif_remove_interface_finish(struct work_struct *work)
+{
+	struct batadv_hard_iface *hard_iface;
+
+	hard_iface = container_of(work, struct batadv_hard_iface,
+				  cleanup_work);
+
+	batadv_sysfs_del_hardif(&hard_iface->hardif_obj);
+	batadv_hardif_free_ref(hard_iface);
+}
+
 static struct batadv_hard_iface *
 batadv_hardif_add_interface(struct net_device *net_dev)
 {
@@ -484,6 +502,9 @@ batadv_hardif_add_interface(struct net_device *net_dev)
 	hard_iface->soft_iface = NULL;
 	hard_iface->if_status = BATADV_IF_NOT_IN_USE;
 	INIT_LIST_HEAD(&hard_iface->list);
+	INIT_WORK(&hard_iface->cleanup_work,
+		  batadv_hardif_remove_interface_finish);
+
 	/* extra reference for return */
 	atomic_set(&hard_iface->refcount, 2);
 
@@ -518,8 +539,7 @@ static void batadv_hardif_remove_interface(struct batadv_hard_iface *hard_iface)
 		return;
 
 	hard_iface->if_status = BATADV_IF_TO_BE_REMOVED;
-	batadv_sysfs_del_hardif(&hard_iface->hardif_obj);
-	batadv_hardif_free_ref(hard_iface);
+	queue_work(batadv_event_workqueue, &hard_iface->cleanup_work);
 }
 
 void batadv_hardif_remove_interfaces(void)

net/batman-adv/soft-interface.c

@@ -449,6 +449,30 @@ static void batadv_interface_setup(struct net_device *dev)
 	memset(priv, 0, sizeof(*priv));
 }
 
+/**
+ * batadv_softif_destroy_finish - cleans up the remains of a softif
+ * @work: work queue item
+ *
+ * Free the parts of the soft interface which can not be removed under
+ * rtnl lock (to prevent deadlock situations).
+ */
+static void batadv_softif_destroy_finish(struct work_struct *work)
+{
+	struct batadv_priv *bat_priv;
+	struct net_device *soft_iface;
+
+	bat_priv = container_of(work, struct batadv_priv,
+				cleanup_work);
+	soft_iface = bat_priv->soft_iface;
+
+	batadv_debugfs_del_meshif(soft_iface);
+	batadv_sysfs_del_meshif(soft_iface);
+
+	rtnl_lock();
+	unregister_netdevice(soft_iface);
+	rtnl_unlock();
+}
+
 struct net_device *batadv_softif_create(const char *name)
 {
 	struct net_device *soft_iface;
@@ -463,6 +487,8 @@ struct net_device *batadv_softif_create(const char *name)
 		goto out;
 
 	bat_priv = netdev_priv(soft_iface);
+	bat_priv->soft_iface = soft_iface;
+	INIT_WORK(&bat_priv->cleanup_work, batadv_softif_destroy_finish);
 
 	/* batadv_interface_stats() needs to be available as soon as
 	 * register_netdevice() has been called
@@ -551,10 +577,10 @@ struct net_device *batadv_softif_create(const char *name)
 
 void batadv_softif_destroy(struct net_device *soft_iface)
 {
-	batadv_debugfs_del_meshif(soft_iface);
-	batadv_sysfs_del_meshif(soft_iface);
+	struct batadv_priv *bat_priv = netdev_priv(soft_iface);
+
 	batadv_mesh_free(soft_iface);
-	unregister_netdevice(soft_iface);
+	queue_work(batadv_event_workqueue, &bat_priv->cleanup_work);
 }
 
 int batadv_softif_is_valid(const struct net_device *net_dev)

net/batman-adv/types.h

@@ -68,6 +68,7 @@ struct batadv_hard_iface_bat_iv {
  * @soft_iface: the batman-adv interface which uses this network interface
  * @rcu: struct used for freeing in an RCU-safe manner
  * @bat_iv: BATMAN IV specific per hard interface data
+ * @cleanup_work: work queue callback item for hard interface deinit
  */
 struct batadv_hard_iface {
 	struct list_head list;
@@ -81,6 +82,7 @@ struct batadv_hard_iface {
 	struct net_device *soft_iface;
 	struct rcu_head rcu;
 	struct batadv_hard_iface_bat_iv bat_iv;
+	struct work_struct cleanup_work;
 };
 
 /**
@@ -428,6 +430,7 @@ struct batadv_priv_dat {
 /**
  * struct batadv_priv - per mesh interface data
  * @mesh_state: current status of the mesh (inactive/active/deactivating)
+ * @soft_iface: net device which holds this struct as private data
  * @stats: structure holding the data for the ndo_get_stats() call
  * @bat_counters: mesh internal traffic statistic counters (see batadv_counters)
  * @aggregated_ogms: bool indicating whether OGM aggregation is enabled
@@ -457,6 +460,7 @@ struct batadv_priv_dat {
  * @forw_bat_list_lock: lock protecting forw_bat_list
  * @forw_bcast_list_lock: lock protecting forw_bcast_list
  * @orig_work: work queue callback item for orig node purging
+ * @cleanup_work: work queue callback item for soft interface deinit
  * @primary_if: one of the hard interfaces assigned to this mesh interface
  *  becomes the primary interface
  * @bat_algo_ops: routing algorithm used by this mesh interface
@@ -469,6 +473,7 @@ struct batadv_priv_dat {
  */
 struct batadv_priv {
 	atomic_t mesh_state;
+	struct net_device *soft_iface;
 	struct net_device_stats stats;
 	uint64_t __percpu *bat_counters; /* Per cpu counters */
 	atomic_t aggregated_ogms;
@@ -502,6 +507,7 @@ struct batadv_priv {
 	spinlock_t forw_bat_list_lock; /* protects forw_bat_list */
 	spinlock_t forw_bcast_list_lock; /* protects forw_bcast_list */
 	struct delayed_work orig_work;
+	struct work_struct cleanup_work;
 	struct batadv_hard_iface __rcu *primary_if;  /* rcu protected pointer */
 	struct batadv_algo_ops *bat_algo_ops;
 #ifdef CONFIG_BATMAN_ADV_BLA