xprtrdma: Fix corner cases when handling device removal

Michal Kalderon has found some corner cases around device unload
with active NFS mounts that I didn't have the imagination to test
when xprtrdma device removal was added last year.

- The ULP device removal handler is responsible for deallocating
  the PD. That wasn't clear to me initially, and my own testing
  suggested it was not necessary, but that is incorrect.

- The transport destruction path can no longer assume that there
  is a valid ID.

- When destroying a transport, ensure that ib_free_cq() is not
  invoked on a CQ that was already released.
Reported-by: Michal Kalderon <Michal.Kalderon@cavium.com>
Fixes: bebd0318 ("xprtrdma: Support unplugging an HCA from ...")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Cc: stable@vger.kernel.org # v4.12+
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/xprtrdma/verbs.c

@@ -250,7 +250,6 @@ rpcrdma_conn_upcall(struct rdma_cm_id *id, struct rdma_cm_event *event)
 		wait_for_completion(&ia->ri_remove_done);
 
 		ia->ri_id = NULL;
-		ia->ri_pd = NULL;
 		ia->ri_device = NULL;
 		/* Return 1 to ensure the core destroys the id. */
 		return 1;
@@ -447,7 +446,9 @@ rpcrdma_ia_remove(struct rpcrdma_ia *ia)
 		ia->ri_id->qp = NULL;
 	}
 	ib_free_cq(ep->rep_attr.recv_cq);
+	ep->rep_attr.recv_cq = NULL;
 	ib_free_cq(ep->rep_attr.send_cq);
+	ep->rep_attr.send_cq = NULL;
 
 	/* The ULP is responsible for ensuring all DMA
 	 * mappings and MRs are gone.
@@ -460,6 +461,8 @@ rpcrdma_ia_remove(struct rpcrdma_ia *ia)
 		rpcrdma_dma_unmap_regbuf(req->rl_recvbuf);
 	}
 	rpcrdma_mrs_destroy(buf);
+	ib_dealloc_pd(ia->ri_pd);
+	ia->ri_pd = NULL;
 
 	/* Allow waiters to continue */
 	complete(&ia->ri_remove_done);
@@ -627,13 +630,15 @@ rpcrdma_ep_destroy(struct rpcrdma_ep *ep, struct rpcrdma_ia *ia)
 {
 	cancel_delayed_work_sync(&ep->rep_connect_worker);
 
-	if (ia->ri_id->qp) {
+	if (ia->ri_id && ia->ri_id->qp) {
 		rpcrdma_ep_disconnect(ep, ia);
 		rdma_destroy_qp(ia->ri_id);
 		ia->ri_id->qp = NULL;
 	}
 
+	if (ep->rep_attr.recv_cq)
 		ib_free_cq(ep->rep_attr.recv_cq);
+	if (ep->rep_attr.send_cq)
 		ib_free_cq(ep->rep_attr.send_cq);
 }