IB/ipoib: Fix ndo_get_iflink

Currently, iflink of the parent interface was always accessed, even
when interface didn't have a parent and hence we crashed there.

Handle the interface types properly: for a child interface, return
the ifindex of the parent, for parent interface, return its ifindex.

For child devices, make sure to set the parent pointer prior to
invoking register_netdevice(), this allows the new ndo to be called
by the stack immediately after the child device is registered.

Fixes: 5aa7add8f14b ('infiniband/ipoib: implement ndo_get_iflink')
Reported-by: Honggang Li <[e-mail]>
Signed-off-by: Erez Shitrit <[e-mail]>
Signed-off-by: Honggang Li <[e-mail]>
Reviewed-By: Jason Gunthorpe <[e-mail]>+
Acked-by: Nicolas Dichtel <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/infiniband/ulp/ipoib/ipoib_main.c

···
 {
 	struct ipoib_dev_priv *priv = netdev_priv(dev);
 
+	/* parent interface */
+	if (!test_bit(IPOIB_FLAG_SUBINTERFACE, &priv->flags))
+		return dev->ifindex;
+
+	/* child/vlan interface */
 	return priv->parent->ifindex;
 }
 

drivers/infiniband/ulp/ipoib/ipoib_vlan.c

···
 	/* MTU will be reset when mcast join happens */
 	priv->dev->mtu   = IPOIB_UD_MTU(priv->max_ib_mtu);
 	priv->mcast_mtu  = priv->admin_mtu = priv->dev->mtu;
+	priv->parent = ppriv->dev;
 	set_bit(IPOIB_FLAG_SUBINTERFACE, &priv->flags);
 
 	result = ipoib_set_dev_features(priv, ppriv->ca);
···
 		ipoib_warn(priv, "failed to initialize; error %i", result);
 		goto register_failed;
 	}
-
-	priv->parent = ppriv->dev;
 
 	ipoib_create_debug_files(priv->dev);