netdev - [PATCH RFC 1/2] tun: don't require serialization lock on tx

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Date:	Wed, 13 Apr 2016 11:04:46 +0200
From:	Paolo Abeni <pabeni@...hat.com>
To:	netdev@...r.kernel.org
Cc:	"David S. Miller" <davem@...emloft.net>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Greg Kurz <gkurz@...ux.vnet.ibm.com>,
	Jason Wang <jasowang@...hat.com>
Subject: [PATCH RFC 1/2] tun: don't require serialization lock on tx

The current tun_net_xmit() implementation don't need any external
lock since it relay on rcu protection for the tun data structure
and on socket queue lock for skb queuing.

This patch set the NETIF_F_LLTX feature bit in the tun device, so
that on xmit, in absence of qdisc, no serialization lock is acquired
by the caller.

Signed-off-by: Paolo Abeni <pabeni@...hat.com>
---
 drivers/net/tun.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index faf9297..42992dc 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1796,7 +1796,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
 		dev->hw_features = NETIF_F_SG | NETIF_F_FRAGLIST |
 				   TUN_USER_FEATURES | NETIF_F_HW_VLAN_CTAG_TX |
 				   NETIF_F_HW_VLAN_STAG_TX;
-		dev->features = dev->hw_features;
+		dev->features = dev->hw_features | NETIF_F_LLTX;
 		dev->vlan_features = dev->features &
 				     ~(NETIF_F_HW_VLAN_CTAG_TX |
 				       NETIF_F_HW_VLAN_STAG_TX);
-- 
1.8.3.1