IB/rxe: Hold refs when running tasklets

It might be possible for all of a QP's references to be dropped
while one of that QP's tasklets is running.

For example, the completer might run during QP destroy.
If qp->valid is false, it will drop all of the packets on
the resp_pkts list, potentially removing the last reference.
Then it tries to advance the SQ consumer pointer. If the
SQ's buffer has already been destroyed, the system will
panic.

To be safe, hold a reference on the QP for the duration
of each tasklet.

Signed-off-by: Andrew Boyer <andrew.boyer@dell.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/sw/rxe/rxe_comp.c

@@ -511,6 +511,8 @@ int rxe_completer(void *arg)
 	struct rxe_pkt_info *pkt = NULL;
 	enum comp_state state;
 
+	rxe_add_ref(qp);
+
 	if (!qp->valid) {
 		while ((skb = skb_dequeue(&qp->resp_pkts))) {
 			rxe_drop_ref(qp);
@@ -740,11 +742,13 @@ int rxe_completer(void *arg)
 	/* we come here if we are done with processing and want the task to
 	 * exit from the loop calling us
 	 */
+	rxe_drop_ref(qp);
 	return -EAGAIN;
 
 done:
 	/* we come here if we have processed a packet we want the task to call
 	 * us again to see if there is anything else to do
 	 */
+	rxe_drop_ref(qp);
 	return 0;
 }

drivers/infiniband/sw/rxe/rxe_req.c

@@ -596,6 +596,8 @@ int rxe_requester(void *arg)
 	struct rxe_send_wqe rollback_wqe;
 	u32 rollback_psn;
 
+	rxe_add_ref(qp);
+
 next_wqe:
 	if (unlikely(!qp->valid || qp->req.state == QP_STATE_ERROR))
 		goto exit;
@@ -750,9 +752,10 @@ int rxe_requester(void *arg)
 		while (rxe_completer(qp) == 0)
 			;
 	}
-
+	rxe_drop_ref(qp);
 	return 0;
 
 exit:
+	rxe_drop_ref(qp);
 	return -EAGAIN;
 }

drivers/infiniband/sw/rxe/rxe_resp.c

@@ -1212,6 +1212,8 @@ int rxe_responder(void *arg)
 	struct rxe_pkt_info *pkt = NULL;
 	int ret = 0;
 
+	rxe_add_ref(qp);
+
 	qp->resp.aeth_syndrome = AETH_ACK_UNLIMITED;
 
 	if (!qp->valid) {
@@ -1400,5 +1402,6 @@ int rxe_responder(void *arg)
 exit:
 	ret = -EAGAIN;
 done:
+	rxe_drop_ref(qp);
 	return ret;
 }