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batman-adv: Avoid recursive call_rcu for batadv_nc_node

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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: d56b1705e2 ("batman-adv: network coding - detect coding nodes and remove these after timeout")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <a@unstable.cc>
This commit is contained in:
Sven Eckelmann 2016-01-05 12:06:19 +01:00 committed by Antonio Quartulli
parent 63b3992722
commit 44e8e7e91d
1 changed files with 8 additions and 11 deletions
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19
net/batman-adv/network-coding.c
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@ -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);
}
/**