net: cls_u32: be more strict about skip-sw flag

Return an error if user requested skip-sw and the underlaying
hardware cannot handle tc offloads (or offloads are disabled).
Signed-off-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sched/cls_u32.c

@@ -457,20 +457,21 @@ static int u32_replace_hw_hnode(struct tcf_proto *tp,
 	struct tc_to_netdev offload;
 	int err;
 
+	if (!tc_should_offload(dev, flags))
+		return tc_skip_sw(flags) ? -EINVAL : 0;
+
 	offload.type = TC_SETUP_CLSU32;
 	offload.cls_u32 = &u32_offload;
 
-	if (tc_should_offload(dev, flags)) {
-		offload.cls_u32->command = TC_CLSU32_NEW_HNODE;
-		offload.cls_u32->hnode.divisor = h->divisor;
-		offload.cls_u32->hnode.handle = h->handle;
-		offload.cls_u32->hnode.prio = h->prio;
+	offload.cls_u32->command = TC_CLSU32_NEW_HNODE;
+	offload.cls_u32->hnode.divisor = h->divisor;
+	offload.cls_u32->hnode.handle = h->handle;
+	offload.cls_u32->hnode.prio = h->prio;
 
-		err = dev->netdev_ops->ndo_setup_tc(dev, tp->q->handle,
-						    tp->protocol, &offload);
-		if (tc_skip_sw(flags))
-			return err;
-	}
+	err = dev->netdev_ops->ndo_setup_tc(dev, tp->q->handle,
+					    tp->protocol, &offload);
+	if (tc_skip_sw(flags))
+		return err;
 
 	return 0;
 }