From: Sven Eckelmann sven@narfation.org
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@narfation.org Signed-off-by: Marek Lindner mareklindner@neomailbox.ch Signed-off-by: Antonio Quartulli a@unstable.cc --- net/batman-adv/network-coding.c | 19 ++++++++----------- 1 file changed, 8 insertions(+), 11 deletions(-)
diff --git a/net/batman-adv/network-coding.c b/net/batman-adv/network-coding.c index c98b0ab85449..cc63b44f0d2e 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); }
/**