RDMA/irdma: Fix possible crash due to NULL netdev in notifier

For some net events in irdma_net_event notifier, the netdev can be NULL
which will cause a crash in rdma_vlan_dev_real_dev.  Fix this by moving
all processing to the NETEVENT_NEIGH_UPDATE case where the netdev is
guaranteed to not be NULL.

Fixes: 6702bc1474 ("RDMA/irdma: Fix netdev notifications for vlan's")
Link: https://lore.kernel.org/r/20220425181703.1634-4-shiraz.saleem@intel.com
Signed-off-by: Mustafa Ismail <mustafa.ismail@intel.com>
Signed-off-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/hw/irdma/utils.c

@@ -258,18 +258,16 @@ int irdma_net_event(struct notifier_block *notifier, unsigned long event,
 	u32 local_ipaddr[4] = {};
 	bool ipv4 = true;
 
-	real_dev = rdma_vlan_dev_real_dev(netdev);
-	if (!real_dev)
-		real_dev = netdev;
-
-	ibdev = ib_device_get_by_netdev(real_dev, RDMA_DRIVER_IRDMA);
-	if (!ibdev)
-		return NOTIFY_DONE;
-
-	iwdev = to_iwdev(ibdev);
-
 	switch (event) {
 	case NETEVENT_NEIGH_UPDATE:
+		real_dev = rdma_vlan_dev_real_dev(netdev);
+		if (!real_dev)
+			real_dev = netdev;
+		ibdev = ib_device_get_by_netdev(real_dev, RDMA_DRIVER_IRDMA);
+		if (!ibdev)
+			return NOTIFY_DONE;
+
+		iwdev = to_iwdev(ibdev);
 		p = (__be32 *)neigh->primary_key;
 		if (neigh->tbl->family == AF_INET6) {
 			ipv4 = false;
@@ -290,13 +288,12 @@ int irdma_net_event(struct notifier_block *notifier, unsigned long event,
 			irdma_manage_arp_cache(iwdev->rf, neigh->ha,
 					       local_ipaddr, ipv4,
 					       IRDMA_ARP_DELETE);
+		ib_device_put(ibdev);
 		break;
 	default:
 		break;
 	}
 
-	ib_device_put(ibdev);
-
 	return NOTIFY_DONE;
 }