netdev - [net-next rfc V3 1/9] macvtap: fix a possible race between queue selection and changing queues

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Date:	Wed,  5 Jun 2013 14:36:24 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	davem@...emloft.net, mst@...hat.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc:	sergei.shtylyov@...entembedded.com,
	Jason Wang <jasowang@...hat.com>
Subject: [net-next rfc V3 1/9] macvtap: fix a possible race between queue selection and changing queues

Complier may generate codes that re-read the vlan->numvtaps during
macvtap_get_queue(). This may lead a race if vlan->numvtaps were changed in the
same time and which can lead unexpected result (e.g. very huge value).

We need prevent the compiler from generating such codes by adding an
ACCESS_ONCE() to make sure vlan->numvtaps were only read once.

Signed-off-by: Jason Wang <jasowang@...hat.com>
---
 drivers/net/macvtap.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 68efb91..5e485e3 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -172,7 +172,7 @@ static struct macvtap_queue *macvtap_get_queue(struct net_device *dev,
 {
 	struct macvlan_dev *vlan = netdev_priv(dev);
 	struct macvtap_queue *tap = NULL;
-	int numvtaps = vlan->numvtaps;
+	int numvtaps = ACCESS_ONCE(vlan->numvtaps);
 	__u32 rxq;
 
 	if (!numvtaps)
-- 
1.7.1

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