mlxsw: spectrum_router: Do not assume RTNL is taken during RIF teardown

IPv6 addresses are deleted in an atomic context, so the driver defers
the potential teardown of the associated router interface (RIF) to a
work item that takes RTNL.

The RIF is only destroyed if the associated netdev does not have any IP
addresses (both IPv4 and IPv6). The IPv4 device ('struct in_device') is
currently fetched via __in_dev_get_rtnl() which assumes RTNL is taken.

Since RTNL is going to be removed, convert it to use __in_dev_get_rcu()
from an RCU read-side critical section.

Note that the IPv6 device ('struct inet6_dev') is fetched via
__in6_dev_get(), which does not require RTNL.
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c

@@ -6285,7 +6285,8 @@ mlxsw_sp_rif_should_config(struct mlxsw_sp_rif *rif, struct net_device *dev,
 	case NETDEV_UP:
 		return rif == NULL;
 	case NETDEV_DOWN:
-		idev = __in_dev_get_rtnl(dev);
+		rcu_read_lock();
+		idev = __in_dev_get_rcu(dev);
 		if (idev && idev->ifa_list)
 			addr_list_empty = false;
 
@@ -6293,6 +6294,7 @@ mlxsw_sp_rif_should_config(struct mlxsw_sp_rif *rif, struct net_device *dev,
 		if (addr_list_empty && inet6_dev &&
 		    !list_empty(&inet6_dev->addr_list))
 			addr_list_empty = false;
+		rcu_read_unlock();
 
 		/* macvlans do not have a RIF, but rather piggy back on the
 		 * RIF of their lower device.