RDMA/rxe: Let destroy qp succeed with stuck packet

In some situations a sent packet may get queued in the NIC longer than
than timeout of a ULP. Currently if this happens the ULP may try to reset
the link by destroying the qp and setting up an alternate connection but
will fail because the rxe driver is waiting for the packet to finish
getting sent and be returned to the skb destructor function where the qp
reference holding things up will be dropped. This patch modifies the way
that the qp is passed to the destructor to pass the qp index and not a qp
pointer. Then the destructor will attempt to lookup the qp from its index
and if it fails exit early. This requires taking a reference on the struct
sock rather than the qp allowing the qp to be destroyed while the sk is
still around waiting for the packet to finish.

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Bob Pearson <[e-mail]>
Signed-off-by: Jason Gunthorpe <[e-mail]>

drivers/infiniband/sw/rxe/rxe_net.c

···
 
 static void rxe_skb_tx_dtor(struct sk_buff *skb)
 {
-	struct sock *sk = skb->sk;
-	struct rxe_qp *qp = sk->sk_user_data;
-	int skb_out = atomic_dec_return(&qp->skb_out);
+	struct net_device *ndev = skb->dev;
+	struct rxe_dev *rxe;
+	unsigned int qp_index;
+	struct rxe_qp *qp;
+	int skb_out;
 
-	if (unlikely(qp->need_req_skb &&
-		     skb_out < RXE_INFLIGHT_SKBS_PER_QP_LOW))
+	rxe = rxe_get_dev_from_net(ndev);
+	if (!rxe && is_vlan_dev(ndev))
+		rxe = rxe_get_dev_from_net(vlan_dev_real_dev(ndev));
+	if (WARN_ON(!rxe))
+		return;
+
+	qp_index = (int)(uintptr_t)skb->sk->sk_user_data;
+	if (!qp_index)
+		return;
+
+	qp = rxe_pool_get_index(&rxe->qp_pool, qp_index);
+	if (!qp)
+		goto put_dev;
+
+	skb_out = atomic_dec_return(&qp->skb_out);
+	if (qp->need_req_skb && skb_out < RXE_INFLIGHT_SKBS_PER_QP_LOW)
 		rxe_sched_task(&qp->send_task);
 
 	rxe_put(qp);
+put_dev:
+	ib_device_put(&rxe->ib_dev);
+	sock_put(skb->sk);
 }
 
 static int rxe_send(struct sk_buff *skb, struct rxe_pkt_info *pkt)
 {
 	int err;
+	struct sock *sk = pkt->qp->sk->sk;
 
+	sock_hold(sk);
+	skb->sk = sk;
 	skb->destructor = rxe_skb_tx_dtor;
-	skb->sk = pkt->qp->sk->sk;
-
-	rxe_get(pkt->qp);
 	atomic_inc(&pkt->qp->skb_out);
 
 	if (skb->protocol == htons(ETH_P_IP))
···
  */
 static int rxe_loopback(struct sk_buff *skb, struct rxe_pkt_info *pkt)
 {
+	struct sock *sk = pkt->qp->sk->sk;
+
 	memcpy(SKB_TO_PKT(skb), pkt, sizeof(*pkt));
 
+	sock_hold(sk);
+	skb->sk = sk;
 	skb->destructor = rxe_skb_tx_dtor;
-	skb->sk = pkt->qp->sk->sk;
-
-	rxe_get(pkt->qp);
 	atomic_inc(&pkt->qp->skb_out);
 
 	if (skb->protocol == htons(ETH_P_IP))

drivers/infiniband/sw/rxe/rxe_qp.c

···
 	err = sock_create_kern(&init_net, AF_INET, SOCK_DGRAM, 0, &qp->sk);
 	if (err < 0)
 		return err;
-	qp->sk->sk->sk_user_data = qp;
+	qp->sk->sk->sk_user_data = (void *)(uintptr_t)qp->elem.index;
 
 	/* pick a source UDP port number for this QP based on
 	 * the source QPN. this spreads traffic for different QPs