linux-kernel - [PATCH 3.16.y-ckt 168/180] batman-adv: Drop immediate batadv_neigh

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Message-Id: <1454538786-12215-169-git-send-email-luis.henriques@canonical.com>
Date:	Wed,  3 Feb 2016 22:32:54 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Sven Eckelmann <sven@...fation.org>,
	Marek Lindner <mareklindner@...mailbox.ch>,
	Antonio Quartulli <a@...table.cc>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 168/180] batman-adv: Drop immediate batadv_neigh_node free function

3.16.7-ckt24 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Sven Eckelmann <sven@...fation.org>

commit 2baa753c276f27f8e844637561ad597867aa6fb6 upstream.

It is not allowed to free the memory of an object which is part of a list
which is protected by rcu-read-side-critical sections without making sure
that no other context is accessing the object anymore. This usually happens
by removing the references to this object and then waiting until the rcu
grace period is over and no one (allowedly) accesses it anymore.

But the _now functions ignore this completely. They free the object
directly even when a different context still tries to access it. This has
to be avoided and thus these functions must be removed and all functions
have to use batadv_neigh_node_free_ref.

Fixes: 89652331c00f ("batman-adv: split tq information in neigh_node struct")
Signed-off-by: Sven Eckelmann <sven@...fation.org>
Signed-off-by: Marek Lindner <mareklindner@...mailbox.ch>
Signed-off-by: Antonio Quartulli <a@...table.cc>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 net/batman-adv/originator.c | 33 ++++++++++-----------------------
 1 file changed, 10 insertions(+), 23 deletions(-)

diff --git a/net/batman-adv/originator.c b/net/batman-adv/originator.c
index f54a1d030647..3390419152d3 100644
--- a/net/batman-adv/originator.c
+++ b/net/batman-adv/originator.c
@@ -210,20 +210,8 @@ static void batadv_neigh_node_free_rcu(struct rcu_head *rcu)
 }
 
 /**
- * batadv_neigh_node_free_ref_now - decrement the neighbors refcounter
- *  and possibly free it (without rcu callback)
- * @neigh_node: neigh neighbor to free
- */
-static void
-batadv_neigh_node_free_ref_now(struct batadv_neigh_node *neigh_node)
-{
-	if (atomic_dec_and_test(&neigh_node->refcount))
-		batadv_neigh_node_free_rcu(&neigh_node->rcu);
-}
-
-/**
  * batadv_neigh_node_free_ref - decrement the neighbors refcounter
- *  and possibly free it
+ *  and possibly release it
  * @neigh_node: neigh neighbor to free
  */
 void batadv_neigh_node_free_ref(struct batadv_neigh_node *neigh_node)
@@ -495,24 +483,23 @@ batadv_neigh_node_get(const struct batadv_orig_node *orig_node,
 }
 
 /**
- * batadv_orig_ifinfo_free_rcu - free the orig_ifinfo object
- * @rcu: rcu pointer of the orig_ifinfo object
+ * batadv_orig_ifinfo_release - release orig_ifinfo from lists and queue for
+ *  free after rcu grace period
+ * @orig_ifinfo: the orig_ifinfo object to release
  */
-static void batadv_orig_ifinfo_free_rcu(struct rcu_head *rcu)
+static void batadv_orig_ifinfo_release(struct batadv_orig_ifinfo *orig_ifinfo)
 {
-	struct batadv_orig_ifinfo *orig_ifinfo;
 	struct batadv_neigh_node *router;
 
-	orig_ifinfo = container_of(rcu, struct batadv_orig_ifinfo, rcu);
-
 	if (orig_ifinfo->if_outgoing != BATADV_IF_DEFAULT)
-		batadv_hardif_free_ref_now(orig_ifinfo->if_outgoing);
+		batadv_hardif_free_ref(orig_ifinfo->if_outgoing);
 
 	/* this is the last reference to this object */
 	router = rcu_dereference_protected(orig_ifinfo->router, true);
 	if (router)
-		batadv_neigh_node_free_ref_now(router);
-	kfree(orig_ifinfo);
+		batadv_neigh_node_free_ref(router);
+
+	kfree_rcu(orig_ifinfo, rcu);
 }
 
 /**
@@ -523,7 +510,7 @@ static void batadv_orig_ifinfo_free_rcu(struct rcu_head *rcu)
 void batadv_orig_ifinfo_free_ref(struct batadv_orig_ifinfo *orig_ifinfo)
 {
 	if (atomic_dec_and_test(&orig_ifinfo->refcount))
-		call_rcu(&orig_ifinfo->rcu, batadv_orig_ifinfo_free_rcu);
+		batadv_orig_ifinfo_release(orig_ifinfo);
 }
 
 /**