RDMA/cxgb4: Keep QP referenced until TID released

The driver is currently releasing the last ref on the QP too early.
This can cause bus errors due to HW still fetching WRs from the HW
queue.  The fix is to keep a qp ref until we release the HW TID.
Signed-off-by: Vipul Pandya <vipul@chelsio.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/hw/cxgb4/cm.c

@@ -143,6 +143,18 @@ static void connect_reply_upcall(struct c4iw_ep *ep, int status);
 static LIST_HEAD(timeout_list);
 static spinlock_t timeout_lock;
 
+static void deref_qp(struct c4iw_ep *ep)
+{
+	c4iw_qp_rem_ref(&ep->com.qp->ibqp);
+	clear_bit(QP_REFERENCED, &ep->com.flags);
+}
+
+static void ref_qp(struct c4iw_ep *ep)
+{
+	set_bit(QP_REFERENCED, &ep->com.flags);
+	c4iw_qp_add_ref(&ep->com.qp->ibqp);
+}
+
 static void start_ep_timer(struct c4iw_ep *ep)
 {
 	PDBG("%s ep %p\n", __func__, ep);
@@ -271,6 +283,8 @@ void _c4iw_free_ep(struct kref *kref)
 
 	ep = container_of(kref, struct c4iw_ep, com.kref);
 	PDBG("%s ep %p state %s\n", __func__, ep, states[state_read(&ep->com)]);
+	if (test_bit(QP_REFERENCED, &ep->com.flags))
+		deref_qp(ep);
 	if (test_bit(RELEASE_RESOURCES, &ep->com.flags)) {
 		cxgb4_remove_tid(ep->com.dev->rdev.lldi.tids, 0, ep->hwtid);
 		dst_release(ep->dst);
@@ -863,7 +877,6 @@ static void close_complete_upcall(struct c4iw_ep *ep)
 		ep->com.cm_id->event_handler(ep->com.cm_id, &event);
 		ep->com.cm_id->rem_ref(ep->com.cm_id);
 		ep->com.cm_id = NULL;
-		ep->com.qp = NULL;
 		set_bit(CLOSE_UPCALL, &ep->com.history);
 	}
 }
@@ -906,7 +919,6 @@ static void peer_abort_upcall(struct c4iw_ep *ep)
 		ep->com.cm_id->event_handler(ep->com.cm_id, &event);
 		ep->com.cm_id->rem_ref(ep->com.cm_id);
 		ep->com.cm_id = NULL;
-		ep->com.qp = NULL;
 		set_bit(ABORT_UPCALL, &ep->com.history);
 	}
 }
@@ -946,7 +958,6 @@ static void connect_reply_upcall(struct c4iw_ep *ep, int status)
 	if (status < 0) {
 		ep->com.cm_id->rem_ref(ep->com.cm_id);
 		ep->com.cm_id = NULL;
-		ep->com.qp = NULL;
 	}
 }
 
@@ -2434,6 +2445,7 @@ int c4iw_accept_cr(struct iw_cm_id *cm_id, struct iw_cm_conn_param *conn_param)
 	cm_id->add_ref(cm_id);
 	ep->com.cm_id = cm_id;
 	ep->com.qp = qp;
+	ref_qp(ep);
 
 	/* bind QP to EP and move to RTS */
 	attrs.mpa_attr = ep->mpa_attr;
@@ -2464,7 +2476,6 @@ int c4iw_accept_cr(struct iw_cm_id *cm_id, struct iw_cm_conn_param *conn_param)
 	return 0;
 err1:
 	ep->com.cm_id = NULL;
-	ep->com.qp = NULL;
 	cm_id->rem_ref(cm_id);
 err:
 	c4iw_put_ep(&ep->com);
@@ -2505,6 +2516,7 @@ int c4iw_connect(struct iw_cm_id *cm_id, struct iw_cm_conn_param *conn_param)
 	ep->com.cm_id = cm_id;
 	ep->com.qp = get_qhp(dev, conn_param->qpn);
 	BUG_ON(!ep->com.qp);
+	ref_qp(ep);
 	PDBG("%s qpn 0x%x qp %p cm_id %p\n", __func__, conn_param->qpn,
 	     ep->com.qp, cm_id);
 

drivers/infiniband/hw/cxgb4/iw_cxgb4.h

@@ -716,6 +716,7 @@ enum c4iw_ep_flags {
 	ABORT_REQ_IN_PROGRESS	= 1,
 	RELEASE_RESOURCES	= 2,
 	CLOSE_SENT		= 3,
+	QP_REFERENCED           = 5,
 };
 
 enum c4iw_ep_history {