Revert "IPoIB: fix mcast_dev_flush/mcast_restart_task race"

This reverts commit e5d1dcf1.

The series of IPoIB bug fixes that went into 3.19-rc1 introduce
regressions, and after trying to sort things out, we decided to revert
to 3.18's IPoIB driver and get things right for 3.20.
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/ulp/ipoib/ipoib_multicast.c

@@ -802,10 +802,7 @@ void ipoib_mcast_dev_flush(struct net_device *dev)
 
 	spin_unlock_irqrestore(&priv->lock, flags);
 
-	/*
-	 * make sure the in-flight joins have finished before we attempt
-	 * to leave
-	 */
+	/* seperate between the wait to the leave*/
 	list_for_each_entry_safe(mcast, tmcast, &remove_list, list)
 		if (test_bit(IPOIB_MCAST_FLAG_BUSY, &mcast->flags))
 			wait_for_completion(&mcast->done);
@@ -926,38 +923,14 @@ void ipoib_mcast_restart_task(struct work_struct *work)
 	netif_addr_unlock(dev);
 	local_irq_restore(flags);
 
-	/*
-	 * make sure the in-flight joins have finished before we attempt
-	 * to leave
-	 */
-	list_for_each_entry_safe(mcast, tmcast, &remove_list, list)
-		if (test_bit(IPOIB_MCAST_FLAG_BUSY, &mcast->flags))
-			wait_for_completion(&mcast->done);
-
-	/*
-	 * We have to cancel outside of the spinlock, but we have to
-	 * take the rtnl lock or else we race with the removal of
-	 * entries from the remove list in mcast_dev_flush as part
-	 * of ipoib_stop() which will call mcast_stop_thread with
-	 * flush == 1 while holding the rtnl lock, and the
-	 * flush_workqueue won't complete until this restart_mcast_task
-	 * completes.  So do like the carrier on task and attempt to
-	 * take the rtnl lock, but if we can't before the ADMIN_UP flag
-	 * goes away, then just return and know that the remove list will
-	 * get flushed later by mcast_dev_flush.
-	 */
-	while (!rtnl_trylock()) {
-		if (!test_bit(IPOIB_FLAG_ADMIN_UP, &priv->flags))
-			return;
-		else
-			msleep(20);
-	}
+	/* We have to cancel outside of the spinlock */
 	list_for_each_entry_safe(mcast, tmcast, &remove_list, list) {
 		ipoib_mcast_leave(mcast->dev, mcast);
 		ipoib_mcast_free(mcast);
 	}
-	ipoib_mcast_start_thread(dev);
-	rtnl_unlock();
+
+	if (test_bit(IPOIB_FLAG_ADMIN_UP, &priv->flags))
+		ipoib_mcast_start_thread(dev);
 }
 
 #ifdef CONFIG_INFINIBAND_IPOIB_DEBUG