IPoIB: protect child list in ipoib_ib_dev_flush

race condition: ipoib_ib_dev_flush is accessing child list without locks.
Signed-off-by: Michael S. Tsirkin <mst@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/ulp/ipoib/ipoib_ib.c

@@ -608,9 +608,13 @@ void ipoib_ib_dev_flush(void *_dev)
 	if (test_bit(IPOIB_FLAG_ADMIN_UP, &priv->flags))
 		ipoib_ib_dev_up(dev);
 
+	down(&priv->vlan_mutex);
+
 	/* Flush any child interfaces too */
 	list_for_each_entry(cpriv, &priv->child_intfs, list)
 		ipoib_ib_dev_flush(&cpriv->dev);
+
+	up(&priv->vlan_mutex);
 }
 
 void ipoib_ib_dev_cleanup(struct net_device *dev)