tipc: eliminate race condition at multicast reception

In a previous commit in this series we resolved a race problem during
unicast message reception.

Here, we resolve the same problem at multicast reception. We apply the
same technique: an input queue serializing the delivery of arriving
buffers. The main difference is that here we do it in two steps.
First, the broadcast link feeds arriving buffers into the tail of an
arrival queue, which head is consumed at the socket level, and where
destination lookup is performed. Second, if the lookup is successful,
the resulting buffer clones are fed into a second queue, the input
queue. This queue is consumed at reception in the socket just like
in the unicast case. Both queues are protected by the same lock, -the
one of the input queue.

Reviewed-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 17 insertions, 0 deletions

diff --git a/net/tipc/msg.h b/net/tipc/msg.h
index ab467261bd9d..9ace47f44a69 100644
--- a/net/tipc/msg.h
+++ b/net/tipc/msg.h
@@ -767,6 +767,23 @@ bool tipc_msg_lookup_dest(struct net *net, struct sk_buff *skb, u32 *dnode,
 			  int *err);
 struct sk_buff *tipc_msg_reassemble(struct sk_buff_head *list);
 
+/* tipc_skb_peek(): peek and reserve first buffer in list
+ * @list: list to be peeked in
+ * Returns pointer to first buffer in list, if any
+ */
+static inline struct sk_buff *tipc_skb_peek(struct sk_buff_head *list,
+					    spinlock_t *lock)
+{
+	struct sk_buff *skb;
+
+	spin_lock_bh(lock);
+	skb = skb_peek(list);
+	if (skb)
+		skb_get(skb);
+	spin_unlock_bh(lock);
+	return skb;
+}
+
 /* tipc_skb_peek_port(): find a destination port, ignoring all destinations
  *                       up to and including 'filter'.
  * Note: ignoring previously tried destinations minimizes the risk of