[linux-next] LinuxNextTracking branch, master, updated. next-20110624

batman at open-mesh.org batman at open-mesh.org
Fri Jun 24 16:09:06 CEST 2011


The following commit has been merged in the master branch:
commit 7d2b554826195372764910da2f0dcb0d9b869108
Author: Marek Lindner <lindner_marek at yahoo.de>
Date:   Thu Feb 10 14:33:50 2011 +0000

    batman-adv: Correct rcu refcounting for softif_neigh
    
    It might be possible that 2 threads access the same data in the same
    rcu grace period. The first thread calls call_rcu() to decrement the
    refcount and free the data while the second thread increases the
    refcount to use the data. To avoid this race condition all refcount
    operations have to be atomic.
    
    Reported-by: Sven Eckelmann <sven at narfation.org>
    Signed-off-by: Marek Lindner <lindner_marek at yahoo.de>

diff --git a/net/batman-adv/soft-interface.c b/net/batman-adv/soft-interface.c
index 7e37077..152beaa 100644
--- a/net/batman-adv/soft-interface.c
+++ b/net/batman-adv/soft-interface.c
@@ -76,20 +76,18 @@ int my_skb_head_push(struct sk_buff *skb, unsigned int len)
 	return 0;
 }
 
-static void softif_neigh_free_ref(struct kref *refcount)
+static void softif_neigh_free_rcu(struct rcu_head *rcu)
 {
 	struct softif_neigh *softif_neigh;
 
-	softif_neigh = container_of(refcount, struct softif_neigh, refcount);
+	softif_neigh = container_of(rcu, struct softif_neigh, rcu);
 	kfree(softif_neigh);
 }
 
-static void softif_neigh_free_rcu(struct rcu_head *rcu)
+static void softif_neigh_free_ref(struct softif_neigh *softif_neigh)
 {
-	struct softif_neigh *softif_neigh;
-
-	softif_neigh = container_of(rcu, struct softif_neigh, rcu);
-	kref_put(&softif_neigh->refcount, softif_neigh_free_ref);
+	if (atomic_dec_and_test(&softif_neigh->refcount))
+		call_rcu(&softif_neigh->rcu, softif_neigh_free_rcu);
 }
 
 void softif_neigh_purge(struct bat_priv *bat_priv)
@@ -116,11 +114,10 @@ void softif_neigh_purge(struct bat_priv *bat_priv)
 				 softif_neigh->addr, softif_neigh->vid);
 			softif_neigh_tmp = bat_priv->softif_neigh;
 			bat_priv->softif_neigh = NULL;
-			kref_put(&softif_neigh_tmp->refcount,
-				 softif_neigh_free_ref);
+			softif_neigh_free_ref(softif_neigh_tmp);
 		}
 
-		call_rcu(&softif_neigh->rcu, softif_neigh_free_rcu);
+		softif_neigh_free_ref(softif_neigh);
 	}
 
 	spin_unlock_bh(&bat_priv->softif_neigh_lock);
@@ -141,8 +138,11 @@ static struct softif_neigh *softif_neigh_get(struct bat_priv *bat_priv,
 		if (softif_neigh->vid != vid)
 			continue;
 
+		if (!atomic_inc_not_zero(&softif_neigh->refcount))
+			continue;
+
 		softif_neigh->last_seen = jiffies;
-		goto found;
+		goto out;
 	}
 
 	softif_neigh = kzalloc(sizeof(struct softif_neigh), GFP_ATOMIC);
@@ -152,15 +152,14 @@ static struct softif_neigh *softif_neigh_get(struct bat_priv *bat_priv,
 	memcpy(softif_neigh->addr, addr, ETH_ALEN);
 	softif_neigh->vid = vid;
 	softif_neigh->last_seen = jiffies;
-	kref_init(&softif_neigh->refcount);
+	/* initialize with 2 - caller decrements counter by one */
+	atomic_set(&softif_neigh->refcount, 2);
 
 	INIT_HLIST_NODE(&softif_neigh->list);
 	spin_lock_bh(&bat_priv->softif_neigh_lock);
 	hlist_add_head_rcu(&softif_neigh->list, &bat_priv->softif_neigh_list);
 	spin_unlock_bh(&bat_priv->softif_neigh_lock);
 
-found:
-	kref_get(&softif_neigh->refcount);
 out:
 	rcu_read_unlock();
 	return softif_neigh;
@@ -264,7 +263,7 @@ static void softif_batman_recv(struct sk_buff *skb, struct net_device *dev,
 			 softif_neigh->addr, softif_neigh->vid);
 		softif_neigh_tmp = bat_priv->softif_neigh;
 		bat_priv->softif_neigh = softif_neigh;
-		kref_put(&softif_neigh_tmp->refcount, softif_neigh_free_ref);
+		softif_neigh_free_ref(softif_neigh_tmp);
 		/* we need to hold the additional reference */
 		goto err;
 	}
@@ -282,7 +281,7 @@ static void softif_batman_recv(struct sk_buff *skb, struct net_device *dev,
 	}
 
 out:
-	kref_put(&softif_neigh->refcount, softif_neigh_free_ref);
+	softif_neigh_free_ref(softif_neigh);
 err:
 	kfree_skb(skb);
 	return;
diff --git a/net/batman-adv/types.h b/net/batman-adv/types.h
index cfbeb45..96f7c22 100644
--- a/net/batman-adv/types.h
+++ b/net/batman-adv/types.h
@@ -268,7 +268,7 @@ struct softif_neigh {
 	uint8_t addr[ETH_ALEN];
 	unsigned long last_seen;
 	short vid;
-	struct kref refcount;
+	atomic_t refcount;
 	struct rcu_head rcu;
 };
 

-- 
LinuxNextTracking


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