IPoIB: Yet another fix for send-only joins

Even after the last fix, it's still possible for a send-only join to
start before the join for the broadcast group has finished.  This
could cause us to create a multicast group using attributes from the
broadcast group that haven't been initialized yet, so we would use
garbage for the Q_Key, etc.  Fix this by waiting until the broadcast
group's attached flag is set before starting send-only joins.

Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/ulp/ipoib/ipoib_multicast.c

@@ -533,8 +533,10 @@ void ipoib_mcast_join_task(void *dev_ptr)
 	}
 
 	if (!priv->broadcast) {
-		priv->broadcast = ipoib_mcast_alloc(dev, 1);
-		if (!priv->broadcast) {
+		struct ipoib_mcast *broadcast;
+
+		broadcast = ipoib_mcast_alloc(dev, 1);
+		if (!broadcast) {
 			ipoib_warn(priv, "failed to allocate broadcast group\n");
 			mutex_lock(&mcast_mutex);
 			if (test_bit(IPOIB_MCAST_RUN, &priv->flags))
@@ -544,10 +546,11 @@ void ipoib_mcast_join_task(void *dev_ptr)
 			return;
 		}
 
-		memcpy(priv->broadcast->mcmember.mgid.raw, priv->dev->broadcast + 4,
+		spin_lock_irq(&priv->lock);
+		memcpy(broadcast->mcmember.mgid.raw, priv->dev->broadcast + 4,
 		       sizeof (union ib_gid));
+		priv->broadcast = broadcast;
 
-		spin_lock_irq(&priv->lock);
 		__ipoib_mcast_add(dev, priv->broadcast);
 		spin_unlock_irq(&priv->lock);
 	}
@@ -701,7 +704,9 @@ void ipoib_mcast_send(struct net_device *dev, union ib_gid *mgid,
 	 */
 	spin_lock(&priv->lock);
 
-	if (!test_bit(IPOIB_MCAST_STARTED, &priv->flags) || !priv->broadcast) {
+	if (!test_bit(IPOIB_MCAST_STARTED, &priv->flags)	||
+	    !priv->broadcast					||
+	    !test_bit(IPOIB_MCAST_FLAG_ATTACHED, &priv->broadcast->flags)) {
 		++priv->stats.tx_dropped;
 		dev_kfree_skb_any(skb);
 		goto unlock;