RE: [v4,net-next,12/15] net: fec: move xdp_rxq_info* APIs out of fec_enet_create_page_pool()

quoted

+static int
+fec_enet_alloc_rxq_buffers(struct net_device *ndev, unsigned int queue)
+{
+	struct fec_enet_private *fep = netdev_priv(ndev);
+	struct fec_enet_priv_rx_q *rxq;
+	int err;
+
+	rxq = fep->rx_queue[queue];
+	err = fec_alloc_rxq_buffers_pp(fep, rxq);
+	if (err)
+		return err;
+
+	err = fec_xdp_rxq_info_reg(fep, rxq);
+	if (err) {
+		fec_free_rxq_buffers(rxq);
+
+		return err;
+	}
+
+	return 0;
+}

Could there be a memory leak here on systems with multiple RX queues? The
old code had:

     err_alloc:
         fec_enet_free_buffers(ndev);
         return -ENOMEM;

which freed all queues (both RX and TX). The new code calls
fec_free_rxq_buffers(rxq), which only frees the current queue.

If fec_enet_alloc_buffers() calls this function in a loop for multiple
queues and queue N fails after queues 0 through N-1 succeeded, only queue
N gets cleaned up. The caller fec_enet_alloc_buffers() just returns
-ENOMEM without freeing the previously allocated queues:

    for (i = 0; i < fep->num_rx_queues; i++)
        if (fec_enet_alloc_rxq_buffers(ndev, i))
            return -ENOMEM;

And fec_enet_open() jumps to err_enet_alloc which does not call
fec_enet_free_buffers(), leaving the page pools and pages from the
successfully allocated queues leaked.

Yes, this is real a potential bug, I will fix it.