IPoIB: Don't start send-only joins while multicast thread is stopped

Fix the following race scenario:
  - Device is up.
  - Port event or set mcast list triggers ipoib_mcast_stop_thread,
    this cancels the query and waits on mcast "done" completion.
  - Completion is called and "done" is set.
  - Meanwhile, ipoib_mcast_send arrives and starts a new query,
    re-initializing "done".

Fix this by adding a "multicast started" bit and checking it before
starting a send-only join.
Signed-off-by: Michael S. Tsirkin <mst@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/ulp/ipoib/ipoib.h

@@ -78,6 +78,7 @@ enum {
 	IPOIB_FLAG_SUBINTERFACE   = 4,
 	IPOIB_MCAST_RUN 	  = 5,
 	IPOIB_STOP_REAPER         = 6,
+	IPOIB_MCAST_STARTED       = 7,
 
 	IPOIB_MAX_BACKOFF_SECONDS = 16,
 

drivers/infiniband/ulp/ipoib/ipoib_multicast.c

@@ -601,6 +601,10 @@ int ipoib_mcast_start_thread(struct net_device *dev)
 		queue_work(ipoib_workqueue, &priv->mcast_task);
 	mutex_unlock(&mcast_mutex);
 
+	spin_lock_irq(&priv->lock);
+	set_bit(IPOIB_MCAST_STARTED, &priv->flags);
+	spin_unlock_irq(&priv->lock);
+
 	return 0;
 }
 
@@ -611,6 +615,10 @@ int ipoib_mcast_stop_thread(struct net_device *dev, int flush)
 
 	ipoib_dbg_mcast(priv, "stopping multicast thread\n");
 
+	spin_lock_irq(&priv->lock);
+	clear_bit(IPOIB_MCAST_STARTED, &priv->flags);
+	spin_unlock_irq(&priv->lock);
+
 	mutex_lock(&mcast_mutex);
 	clear_bit(IPOIB_MCAST_RUN, &priv->flags);
 	cancel_delayed_work(&priv->mcast_task);
@@ -693,6 +701,12 @@ 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->stats.tx_dropped;
+		dev_kfree_skb_any(skb);
+		goto unlock;
+	}
+
 	mcast = __ipoib_mcast_find(dev, mgid);
 	if (!mcast) {
 		/* Let's create a new send only group now */
@@ -754,6 +768,7 @@ void ipoib_mcast_send(struct net_device *dev, union ib_gid *mgid,
 		ipoib_send(dev, skb, mcast->ah, IB_MULTICAST_QPN);
 	}
 
+unlock:
 	spin_unlock(&priv->lock);
 }