IB/rxe: Move refcounting earlier in rxe_send()

The network stack will call nskb's destructor, rxe_skb_tx_dtor(), if the
packet gets dropped by ip_local_out()/ip6_local_out(). Thus we need to add
the QP ref before output to avoid extra dereferences during network
congestion. This could lead to unwanted destruction of the QP.

Fix up the skb_out accounting, too.

Fixes: fda85ce91240 ("IB/rxe: Fix kernel panic from skb destructor")
Signed-off-by: Andrew Boyer <andrew.boyer@dell.com>
Acked-by: Moni Shoua <monis@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/sw/rxe/rxe_net.c

@@ -460,12 +460,17 @@ int rxe_send(struct rxe_dev *rxe, struct rxe_pkt_info *pkt, struct sk_buff *skb)
 	nskb->destructor = rxe_skb_tx_dtor;
 	nskb->sk = pkt->qp->sk->sk;
 
+	rxe_add_ref(pkt->qp);
+	atomic_inc(&pkt->qp->skb_out);
+
 	if (av->network_type == RDMA_NETWORK_IPV4) {
 		err = ip_local_out(dev_net(skb_dst(skb)->dev), nskb->sk, nskb);
 	} else if (av->network_type == RDMA_NETWORK_IPV6) {
 		err = ip6_local_out(dev_net(skb_dst(skb)->dev), nskb->sk, nskb);
 	} else {
 		pr_err("Unknown layer 3 protocol: %d\n", av->network_type);
+		atomic_dec(&pkt->qp->skb_out);
+		rxe_drop_ref(pkt->qp);
 		kfree_skb(nskb);
 		return -EINVAL;
 	}
@@ -475,10 +480,7 @@ int rxe_send(struct rxe_dev *rxe, struct rxe_pkt_info *pkt, struct sk_buff *skb)
 		return -EAGAIN;
 	}
 
-	rxe_add_ref(pkt->qp);
-	atomic_inc(&pkt->qp->skb_out);
 	kfree_skb(skb);
-
 	return 0;
 }