netdev - [PATCH net-next] tun: avoid unnecessary READ_ONCE in tun_net

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Date:   Tue,  5 Dec 2017 22:11:17 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     netdev@...r.kernel.org
Cc:     jasowang@...hat.com, davem@...emloft.net,
        Willem de Bruijn <willemb@...gle.com>
Subject: [PATCH net-next] tun: avoid unnecessary READ_ONCE in tun_net_xmit

From: Willem de Bruijn <willemb@...gle.com>

The statement no longer serves a purpose.

Commit fa35864e0bb7 ("tuntap: Fix for a race in accessing numqueues")
added the ACCESS_ONCE to avoid a race condition with skb_queue_len.

Commit 436accebb530 ("tuntap: remove unnecessary sk_receive_queue
length check during xmit") removed the affected skb_queue_len check.

Commit 96f84061620c ("tun: add eBPF based queue selection method")
split the function, reading the field a second time in the callee.
The temp variable is now only read once, so just remove it.

Signed-off-by: Willem de Bruijn <willemb@...gle.com>
---
 drivers/net/tun.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 787cc35ef89b..c2ad8f3858d1 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -990,14 +990,12 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
 	struct tun_struct *tun = netdev_priv(dev);
 	int txq = skb->queue_mapping;
 	struct tun_file *tfile;
-	u32 numqueues = 0;

 	rcu_read_lock();
 	tfile = rcu_dereference(tun->tfiles[txq]);
-	numqueues = READ_ONCE(tun->numqueues);

 	/* Drop packet if interface is not attached */
-	if (txq >= numqueues)
+	if (txq >= tun->numqueues)
 		goto drop;

 	if (!rcu_dereference(tun->steering_prog))
-- 
2.15.1.424.g9478a66081-goog