xprtrdma: Fix recursion into rpcrdma_xprt_disconnect()

Both Dan and I have observed two processes invoking
rpcrdma_xprt_disconnect() concurrently. In my case:

1. The connect worker invokes rpcrdma_xprt_disconnect(), which
   drains the QP and waits for the final completion
2. This causes the newly posted Receive to flush and invoke
   xprt_force_disconnect()
3. xprt_force_disconnect() sets CLOSE_WAIT and wakes up the RPC task
   that is holding the transport lock
4. The RPC task invokes xprt_connect(), which calls ->ops->close
5. xprt_rdma_close() invokes rpcrdma_xprt_disconnect(), which tries
   to destroy the QP.

Deadlock.

To prevent xprt_force_disconnect() from waking anything, handle the
clean up after a failed connection attempt in the xprt's sndtask.

The retry loop is removed from rpcrdma_xprt_connect() to ensure
that the newly allocated ep and id are properly released before
a REJECTED connection attempt can be retried.

Reported-by: Dan Aloni <dan@kernelim.com>
Fixes: e28ce90 ("xprtrdma: kmalloc rpcrdma_ep separate from rpcrdma_xprt")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

net/sunrpc/xprtrdma/transport.c

@@ -249,6 +249,11 @@ xprt_rdma_connect_worker(struct work_struct *work)
 					   xprt->stat.connect_start;
 		xprt_set_connected(xprt);
 		rc = -EAGAIN;
+	} else {
+		/* Force a call to xprt_rdma_close to clean up */
+		spin_lock(&xprt->transport_lock);
+		set_bit(XPRT_CLOSE_WAIT, &xprt->state);
+		spin_unlock(&xprt->transport_lock);
 	}
 	xprt_wake_pending_tasks(xprt, rc);
 }

net/sunrpc/xprtrdma/verbs.c

@@ -290,7 +290,7 @@ rpcrdma_cm_event_handler(struct rdma_cm_id *id, struct rdma_cm_event *event)
 			sap, rdma_reject_msg(id, event->status));
 		ep->re_connect_status = -ECONNREFUSED;
 		if (event->status == IB_CM_REJ_STALE_CONN)
-			ep->re_connect_status = -EAGAIN;
+			ep->re_connect_status = -ENOTCONN;
 		goto disconnected;
 	case RDMA_CM_EVENT_DISCONNECTED:
 		ep->re_connect_status = -ECONNABORTED;
@@ -521,8 +521,6 @@ int rpcrdma_xprt_connect(struct rpcrdma_xprt *r_xprt)
 	struct rpcrdma_ep *ep;
 	int rc;
 
-retry:
-	rpcrdma_xprt_disconnect(r_xprt);
 	rc = rpcrdma_ep_create(r_xprt);
 	if (rc)
 		return rc;
@@ -550,17 +548,13 @@ int rpcrdma_xprt_connect(struct rpcrdma_xprt *r_xprt)
 	wait_event_interruptible(ep->re_connect_wait,
 				 ep->re_connect_status != 0);
 	if (ep->re_connect_status <= 0) {
-		if (ep->re_connect_status == -EAGAIN)
-			goto retry;
 		rc = ep->re_connect_status;
 		goto out;
 	}
 
 	rc = rpcrdma_reqs_setup(r_xprt);
-	if (rc) {
-		rpcrdma_xprt_disconnect(r_xprt);
+	if (rc)
 		goto out;
-	}
 	rpcrdma_mrs_create(r_xprt);
 
 out: