[linux-next] LinuxNextTracking branch, master, updated. next-20160118

batman at open-mesh.org batman at open-mesh.org
Tue Jan 19 00:15:45 CET 2016


The following commit has been merged in the master branch:
commit 44e8e7e91d6c7c7ab19688750f7257292640d1a0
Author: Sven Eckelmann <sven at narfation.org>
Date:   Tue Jan 5 12:06:19 2016 +0100

    batman-adv: Avoid recursive call_rcu for batadv_nc_node
    
    The batadv_nc_node_free_ref function uses call_rcu to delay the free of the
    batadv_nc_node object until no (already started) rcu_read_lock is enabled
    anymore. This makes sure that no context is still trying to access the
    object which should be removed. But batadv_nc_node also contains a
    reference to orig_node which must be removed.
    
    The reference drop of orig_node was done in the call_rcu function
    batadv_nc_node_free_rcu but should actually be done in the
    batadv_nc_node_release function to avoid nested call_rcus. This is
    important because rcu_barrier (e.g. batadv_softif_free or batadv_exit) will
    not detect the inner call_rcu as relevant for its execution. Otherwise this
    barrier will most likely be inserted in the queue before the callback of
    the first call_rcu was executed. The caller of rcu_barrier will therefore
    continue to run before the inner call_rcu callback finished.
    
    Fixes: d56b1705e28c ("batman-adv: network coding - detect coding nodes and remove these after timeout")
    Signed-off-by: Sven Eckelmann <sven at narfation.org>
    Signed-off-by: Marek Lindner <mareklindner at neomailbox.ch>
    Signed-off-by: Antonio Quartulli <a at unstable.cc>

diff --git a/net/batman-adv/network-coding.c b/net/batman-adv/network-coding.c
index c98b0ab..cc63b44 100644
--- a/net/batman-adv/network-coding.c
+++ b/net/batman-adv/network-coding.c
@@ -203,28 +203,25 @@ void batadv_nc_init_orig(struct batadv_orig_node *orig_node)
 }
 
 /**
- * batadv_nc_node_free_rcu - rcu callback to free an nc node and remove
- *  its refcount on the orig_node
- * @rcu: rcu pointer of the nc node
+ * batadv_nc_node_release - release nc_node from lists and queue for free after
+ *  rcu grace period
+ * @nc_node: the nc node to free
  */
-static void batadv_nc_node_free_rcu(struct rcu_head *rcu)
+static void batadv_nc_node_release(struct batadv_nc_node *nc_node)
 {
-	struct batadv_nc_node *nc_node;
-
-	nc_node = container_of(rcu, struct batadv_nc_node, rcu);
 	batadv_orig_node_free_ref(nc_node->orig_node);
-	kfree(nc_node);
+	kfree_rcu(nc_node, rcu);
 }
 
 /**
- * batadv_nc_node_free_ref - decrements the nc node refcounter and possibly
- * frees it
+ * batadv_nc_node_free_ref - decrement the nc node refcounter and possibly
+ *  release it
  * @nc_node: the nc node to free
  */
 static void batadv_nc_node_free_ref(struct batadv_nc_node *nc_node)
 {
 	if (atomic_dec_and_test(&nc_node->refcount))
-		call_rcu(&nc_node->rcu, batadv_nc_node_free_rcu);
+		batadv_nc_node_release(nc_node);
 }
 
 /**

-- 
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