Patch "batman-adv: Avoid recursive call_rcu for batadv_bla_claim" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

batman-adv: Avoid recursive call_rcu for batadv_bla_claim

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
batman-adv-avoid-recursive-call_rcu-for-batadv_bla_claim.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Sven Eckelmann <[email protected]>
Date: Thu, 14 Jan 2016 15:28:19 +0100
Subject: batman-adv: Avoid recursive call_rcu for batadv_bla_claim

From: Sven Eckelmann <[email protected]>

[ Upstream commit 63b399272294e7a939cde41792dca38c549f0484 ]

The batadv_claim_free_ref function uses call_rcu to delay the free of the batadv_bla_claim 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_bla_claim also contains a reference to backbone_gw which must be removed.

The reference drop of backbone_gw was done in the call_rcu function batadv_claim_free_rcu but should actually be done in the batadv_claim_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.

---
 net/batman-adv/bridge_loop_avoidance.c |   10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

@@ -127,21 +127,17 @@ batadv_backbone_gw_free_ref(struct batad
 }
 
 /* finally deinitialize the claim */
-static void batadv_claim_free_rcu(struct rcu_head *rcu)
+static void batadv_claim_release(struct batadv_bla_claim *claim)
 {
-	struct batadv_bla_claim *claim;
-
-	claim = container_of(rcu, struct batadv_bla_claim, rcu);
-
 	batadv_backbone_gw_free_ref(claim->backbone_gw);
-	kfree(claim);
+	kfree_rcu(claim, rcu);
 }
 
 /* free a claim, call claim_free_rcu if its the last reference */
 static void batadv_claim_free_ref(struct batadv_bla_claim *claim)
 {
 	if (atomic_dec_and_test(&claim->refcount))
-		call_rcu(&claim->rcu, batadv_claim_free_rcu);
+		batadv_claim_release(claim);
 }
 
 /**

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/batman-adv-drop-immediate-batadv_neigh_node-free-function.patch queue-4.4/batman-adv-drop-immediate-neigh_ifinfo-free-function.patch queue-4.4/batman-adv-drop-immediate-orig_node-free-function.patch queue-4.4/batman-adv-drop-immediate-batadv_orig_ifinfo-free-function.patch queue-4.4/batman-adv-avoid-recursive-call_rcu-for-batadv_nc_node.patch queue-4.4/batman-adv-drop-immediate-batadv_hard_iface-free-function.patch queue-4.4/batman-adv-avoid-recursive-call_rcu-for-batadv_bla_claim.patch