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>

1 files changed, 29 insertions, 3 deletions

diff --git a/net/batman-adv/soft-interface.c b/net/batman-adv/soft-interface.c
index 3d6816667bfc..c9962fee44b1 100644
--- a/net/batman-adv/soft-interface.c
+++ b/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 @@ out:
 
 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)