xsk: refactor xdp_umem_assign_dev()

Return early and only take the ref on dev once there is no possibility
of failing.
Signed-off-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: NQuentin Monnet <quentin.monnet@netronome.com>
Acked-by: NBjörn Töpel <bjorn.topel@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/xdp/xdp_umem.c

@@ -56,19 +56,17 @@ int xdp_umem_assign_dev(struct xdp_umem *umem, struct net_device *dev,
 	if (force_copy)
 		return 0;
 
-	dev_hold(dev);
+	if (!dev->netdev_ops->ndo_bpf || !dev->netdev_ops->ndo_xsk_async_xmit)
+		return force_zc ? -ENOTSUPP : 0; /* fail or fallback */
 
-	if (dev->netdev_ops->ndo_bpf && dev->netdev_ops->ndo_xsk_async_xmit) {
 	bpf.command = XDP_QUERY_XSK_UMEM;
 
 	rtnl_lock();
 	err = dev->netdev_ops->ndo_bpf(dev, &bpf);
 	rtnl_unlock();
 
-		if (err) {
-			dev_put(dev);
+	if (err)
 		return force_zc ? -ENOTSUPP : 0;
-		}
 
 	bpf.command = XDP_SETUP_XSK_UMEM;
 	bpf.xsk.umem = umem;
@@ -78,19 +76,14 @@ int xdp_umem_assign_dev(struct xdp_umem *umem, struct net_device *dev,
 	err = dev->netdev_ops->ndo_bpf(dev, &bpf);
 	rtnl_unlock();
 
-		if (err) {
-			dev_put(dev);
+	if (err)
 		return force_zc ? err : 0; /* fail or fallback */
-		}
 
+	dev_hold(dev);
 	umem->dev = dev;
 	umem->queue_id = queue_id;
 	umem->zc = true;
 	return 0;
-	}
-
-	dev_put(dev);
-	return force_zc ? -ENOTSUPP : 0; /* fail or fallback */
 }
 
 static void xdp_umem_clear_dev(struct xdp_umem *umem)