net: thunderx: nicvf_xdp_setup error code path

[Lorenzo Bianconi <lorenzo.bianconi@redhat.com>]

Hi all,

looking at thunderx XDP support I noticed that nic->xdp_prog pointer in
nicvf_xdp_setup is not actually set to NULL if bpf_prog_add fails but it
is initialized with bpf_prog_add error code. xdp_prog pointer value is used in
the driver to verify if XDP is currently enabled.
Moreover nicvf_xdp_setup does not report to the userspace any error code in
case of failure.
I wrote the following patch to fix the reported issues. Please note I just
compiled it, not actually tested since I have no thunderx nic at the moment.

@Sunil: could you please give it a whirl? If it is ok I will post a formal
patch, thanks

Regards,
Lorenzo

diff --git a/drivers/net/ethernet/cavium/thunder/nicvf_main.c b/drivers/net/ethernet/cavium/thunder/nicvf_main.c
index 768f584f8392..88f8a8fa93cd 100644
--- a/drivers/net/ethernet/cavium/thunder/nicvf_main.c
+++ b/drivers/net/ethernet/cavium/thunder/nicvf_main.c
@@ -1784,6 +1784,7 @@ static int nicvf_xdp_setup(struct nicvf *nic, struct bpf_prog *prog)
 	bool if_up = netif_running(nic->netdev);
 	struct bpf_prog *old_prog;
 	bool bpf_attached = false;
+	int ret = 0;
 
 	/* For now just support only the usual MTU sized frames */
 	if (prog && (dev->mtu > 1500)) {
@@ -1817,8 +1818,12 @@ static int nicvf_xdp_setup(struct nicvf *nic, struct bpf_prog *prog)
 	if (nic->xdp_prog) {
 		/* Attach BPF program */
 		nic->xdp_prog = bpf_prog_add(nic->xdp_prog, nic->rx_queues - 1);
-		if (!IS_ERR(nic->xdp_prog))
+		if (!IS_ERR(nic->xdp_prog)) {
 			bpf_attached = true;
+		} else {
+			ret = PTR_ERR(nic->xdp_prog);
+			nic->xdp_prog = NULL;
+		}
 	}
 
 	/* Calculate Tx queues needed for XDP and network stack */
@@ -1830,7 +1835,7 @@ static int nicvf_xdp_setup(struct nicvf *nic, struct bpf_prog *prog)
 		netif_trans_update(nic->netdev);
 	}
 
-	return 0;
+	return ret;
 }
 
 static int nicvf_xdp(struct net_device *netdev, struct netdev_bpf *xdp)