netdev - [RFC bpf-next 2/6] xsk: refactor xdp_umem_assign

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Message-Id: <20180726214148.2087-3-jakub.kicinski@netronome.com>
Date:   Thu, 26 Jul 2018 14:41:44 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     alexei.starovoitov@...il.com, daniel@...earbox.net,
        brouer@...hat.com,
        Björn Töpel <bjorn.topel@...el.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>
Cc:     oss-drivers@...ronome.com, netdev@...r.kernel.org,
        Jakub Kicinski <jakub.kicinski@...ronome.com>
Subject: [RFC bpf-next 2/6] 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: Jakub Kicinski <jakub.kicinski@...ronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@...ronome.com>
---
 net/xdp/xdp_umem.c | 49 ++++++++++++++++++++--------------------------
 1 file changed, 21 insertions(+), 28 deletions(-)

diff --git a/net/xdp/xdp_umem.c b/net/xdp/xdp_umem.c
index f47abb46c587..c199d66b5f3f 100644
--- a/net/xdp/xdp_umem.c
+++ b/net/xdp/xdp_umem.c
@@ -56,41 +56,34 @@ 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;
+	bpf.command = XDP_QUERY_XSK_UMEM;
 
-		rtnl_lock();
-		err = dev->netdev_ops->ndo_bpf(dev, &bpf);
-		rtnl_unlock();
+	rtnl_lock();
+	err = dev->netdev_ops->ndo_bpf(dev, &bpf);
+	rtnl_unlock();
 
-		if (err) {
-			dev_put(dev);
-			return force_zc ? -ENOTSUPP : 0;
-		}
+	if (err)
+		return force_zc ? -ENOTSUPP : 0;
 
-		bpf.command = XDP_SETUP_XSK_UMEM;
-		bpf.xsk.umem = umem;
-		bpf.xsk.queue_id = queue_id;
+	bpf.command = XDP_SETUP_XSK_UMEM;
+	bpf.xsk.umem = umem;
+	bpf.xsk.queue_id = queue_id;
 
-		rtnl_lock();
-		err = dev->netdev_ops->ndo_bpf(dev, &bpf);
-		rtnl_unlock();
+	rtnl_lock();
+	err = dev->netdev_ops->ndo_bpf(dev, &bpf);
+	rtnl_unlock();
 
-		if (err) {
-			dev_put(dev);
-			return force_zc ? err : 0; /* fail or fallback */
-		}
-
-		umem->dev = dev;
-		umem->queue_id = queue_id;
-		umem->zc = true;
-		return 0;
-	}
+	if (err)
+		return force_zc ? err : 0; /* fail or fallback */
 
-	dev_put(dev);
-	return force_zc ? -ENOTSUPP : 0; /* fail or fallback */
+	dev_hold(dev);
+	umem->dev = dev;
+	umem->queue_id = queue_id;
+	umem->zc = true;
+	return 0;
 }
 
 static void xdp_umem_clear_dev(struct xdp_umem *umem)
-- 
2.17.1