i40iw: Do an RCU lookup in i40iw_add_ipv4_addr

The in_dev_for_each_ifa_rtnl() iterator in i40iw_add_ipv4_addr requires
that the rtnl lock be held. But the rtnl_trylock/unlock scheme in this
function does not guarantee it.

Replace the rtnl locking with an RCU lookup using
in_dev_for_each_ifa_rcu()

Fixes: 8e06af71 ("i40iw: add main, hdr, status")
Link: https://lore.kernel.org/r/20200204223840.2151-1-shiraz.saleem@intel.comSigned-off-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/i40iw/i40iw_main.c

@@ -1212,22 +1212,19 @@ static void i40iw_add_ipv4_addr(struct i40iw_device *iwdev)
 {
 	struct net_device *dev;
 	struct in_device *idev;
-	bool got_lock = true;
 	u32 ip_addr;
 
-	if (!rtnl_trylock())
-		got_lock = false;
-
-	for_each_netdev(&init_net, dev) {
+	rcu_read_lock();
+	for_each_netdev_rcu(&init_net, dev) {
 		if ((((rdma_vlan_dev_vlan_id(dev) < 0xFFFF) &&
 		      (rdma_vlan_dev_real_dev(dev) == iwdev->netdev)) ||
-		    (dev == iwdev->netdev)) && (dev->flags & IFF_UP)) {
+		    (dev == iwdev->netdev)) && (READ_ONCE(dev->flags) & IFF_UP)) {
 			const struct in_ifaddr *ifa;
 
-			idev = in_dev_get(dev);
+			idev = __in_dev_get_rcu(dev);
 			if (!idev)
 				continue;
-			in_dev_for_each_ifa_rtnl(ifa, idev) {
+			in_dev_for_each_ifa_rcu(ifa, idev) {
 				i40iw_debug(&iwdev->sc_dev, I40IW_DEBUG_CM,
 					    "IP=%pI4, vlan_id=%d, MAC=%pM\n", &ifa->ifa_address,
 					     rdma_vlan_dev_vlan_id(dev), dev->dev_addr);
@@ -1239,12 +1236,9 @@ static void i40iw_add_ipv4_addr(struct i40iw_device *iwdev)
 						       true,
 						       I40IW_ARP_ADD);
 			}
-
-			in_dev_put(idev);
 		}
 	}
-	if (got_lock)
-		rtnl_unlock();
+	rcu_read_unlock();
 }
 
 /**