RDMA/cxgb4: Fix race in fini path

There exists a race condition where the app disconnects, which
initiates an orderly close (via rdma_fini()), concurrently with an
ingress abort condition, which initiates an abortive close operation.
Since rdma_fini() must be called without IRQs disabled, the fini can
be called after the QP has been transitioned to ERROR.  This is ok,
but we need to protect against qp->ep getting NULLed.

Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/cxgb4/qp.c

@@ -961,28 +961,29 @@ static void flush_qp(struct c4iw_qp *qhp, unsigned long *flag)
 	__flush_qp(qhp, rchp, schp, flag);
 }
 
-static int rdma_fini(struct c4iw_dev *rhp, struct c4iw_qp *qhp)
+static int rdma_fini(struct c4iw_dev *rhp, struct c4iw_qp *qhp,
+		     struct c4iw_ep *ep)
 {
 	struct fw_ri_wr *wqe;
 	int ret;
 	struct c4iw_wr_wait wr_wait;
 	struct sk_buff *skb;
 
 	PDBG("%s qhp %p qid 0x%x tid %u\n", __func__, qhp, qhp->wq.sq.qid,
-	     qhp->ep->hwtid);
+	     ep->hwtid);
 
 	skb = alloc_skb(sizeof *wqe, GFP_KERNEL);
 	if (!skb)
 		return -ENOMEM;
-	set_wr_txq(skb, CPL_PRIORITY_DATA, qhp->ep->txq_idx);
+	set_wr_txq(skb, CPL_PRIORITY_DATA, ep->txq_idx);
 
 	wqe = (struct fw_ri_wr *)__skb_put(skb, sizeof(*wqe));
 	memset(wqe, 0, sizeof *wqe);
 	wqe->op_compl = cpu_to_be32(
 		FW_WR_OP(FW_RI_INIT_WR) |
 		FW_WR_COMPL(1));
 	wqe->flowid_len16 = cpu_to_be32(
-		FW_WR_FLOWID(qhp->ep->hwtid) |
+		FW_WR_FLOWID(ep->hwtid) |
 		FW_WR_LEN16(DIV_ROUND_UP(sizeof *wqe, 16)));
 	wqe->cookie = (u64)&wr_wait;
 
@@ -1212,17 +1213,16 @@ int c4iw_modify_qp(struct c4iw_dev *rhp, struct c4iw_qp *qhp,
 		case C4IW_QP_STATE_CLOSING:
 			BUG_ON(atomic_read(&qhp->ep->com.kref.refcount) < 2);
 			qhp->attr.state = C4IW_QP_STATE_CLOSING;
+			ep = qhp->ep;
 			if (!internal) {
 				abort = 0;
 				disconnect = 1;
-				ep = qhp->ep;
 				c4iw_get_ep(&ep->com);
 			}
 			spin_unlock_irqrestore(&qhp->lock, flag);
-			ret = rdma_fini(rhp, qhp);
+			ret = rdma_fini(rhp, qhp, ep);
 			spin_lock_irqsave(&qhp->lock, flag);
 			if (ret) {
-				ep = qhp->ep;
 				c4iw_get_ep(&ep->com);
 				disconnect = abort = 1;
 				goto err;