net: enetc: recalculate num_real_tx_queues when XDP program attaches

Since the blamed net-next commit, enetc_setup_xdp_prog() no longer goes
through enetc_open(), and therefore, the function which was supposed to
detect whether a BPF program exists (in order to crop some TX queues
from network stack usage), enetc_num_stack_tx_queues(), no longer gets
called.

We can move the netif_set_real_num_rx_queues() call to enetc_alloc_msix()
(probe time), since it is a runtime invariant. We can do the same thing
with netif_set_real_num_tx_queues(), and let enetc_reconfigure_xdp_cb()
explicitly recalculate and change the number of stack TX queues.

Fixes: c33bfaf9 ("net: enetc: set up XDP program under enetc_reconfigure()")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/freescale/enetc/enetc.c

@@ -2454,7 +2454,6 @@ int enetc_open(struct net_device *ndev)
 {
 	struct enetc_ndev_priv *priv = netdev_priv(ndev);
 	struct enetc_bdr_resource *tx_res, *rx_res;
-	int num_stack_tx_queues;
 	bool extended;
 	int err;
 
@@ -2480,16 +2479,6 @@ int enetc_open(struct net_device *ndev)
 		goto err_alloc_rx;
 	}
 
-	num_stack_tx_queues = enetc_num_stack_tx_queues(priv);
-
-	err = netif_set_real_num_tx_queues(ndev, num_stack_tx_queues);
-	if (err)
-		goto err_set_queues;
-
-	err = netif_set_real_num_rx_queues(ndev, priv->num_rx_rings);
-	if (err)
-		goto err_set_queues;
-
 	enetc_tx_onestep_tstamp_init(priv);
 	enetc_assign_tx_resources(priv, tx_res);
 	enetc_assign_rx_resources(priv, rx_res);
@@ -2498,8 +2487,6 @@ int enetc_open(struct net_device *ndev)
 
 	return 0;
 
-err_set_queues:
-	enetc_free_rx_resources(rx_res, priv->num_rx_rings);
 err_alloc_rx:
 	enetc_free_tx_resources(tx_res, priv->num_tx_rings);
 err_alloc_tx:
@@ -2683,9 +2670,18 @@ EXPORT_SYMBOL_GPL(enetc_setup_tc_mqprio);
 static int enetc_reconfigure_xdp_cb(struct enetc_ndev_priv *priv, void *ctx)
 {
 	struct bpf_prog *old_prog, *prog = ctx;
-	int i;
+	int num_stack_tx_queues;
+	int err, i;
 
 	old_prog = xchg(&priv->xdp_prog, prog);
+
+	num_stack_tx_queues = enetc_num_stack_tx_queues(priv);
+	err = netif_set_real_num_tx_queues(priv->ndev, num_stack_tx_queues);
+	if (err) {
+		xchg(&priv->xdp_prog, old_prog);
+		return err;
+	}
+
 	if (old_prog)
 		bpf_prog_put(old_prog);
 
@@ -2906,6 +2902,7 @@ EXPORT_SYMBOL_GPL(enetc_ioctl);
 int enetc_alloc_msix(struct enetc_ndev_priv *priv)
 {
 	struct pci_dev *pdev = priv->si->pdev;
+	int num_stack_tx_queues;
 	int first_xdp_tx_ring;
 	int i, n, err, nvec;
 	int v_tx_rings;
@@ -2982,6 +2979,16 @@ int enetc_alloc_msix(struct enetc_ndev_priv *priv)
 		}
 	}
 
+	num_stack_tx_queues = enetc_num_stack_tx_queues(priv);
+
+	err = netif_set_real_num_tx_queues(priv->ndev, num_stack_tx_queues);
+	if (err)
+		goto fail;
+
+	err = netif_set_real_num_rx_queues(priv->ndev, priv->num_rx_rings);
+	if (err)
+		goto fail;
+
 	first_xdp_tx_ring = priv->num_tx_rings - num_possible_cpus();
 	priv->xdp_tx_ring = &priv->tx_ring[first_xdp_tx_ring];