[PATCH] Don't allow sharing of tx skbs on xen-netfront

[Neil Horman <nhorman@tuxdriver.com>]

It was pointed out to me recently that the xen-netfront driver can't safely
support shared skbs on transmit, since, while it doesn't maintain skb state
directly, it does pass a pointer to the skb to the hypervisor via a list, and
the hypervisor may expect the contents of the skb to remain stable.  Clearing
the IFF_TX_SKB_SHARING flag after the call to alloc_etherdev to make it safe.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: "David S. Miller" <davem@davemloft.net>
CC: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
CC: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
CC: xen-devel@lists.xensource.com
---
 drivers/net/xen-netfront.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 226faab..fb1077b 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -1252,6 +1252,12 @@ static struct net_device * __devinit xennet_create_dev(struct xenbus_device *dev
 		return ERR_PTR(-ENOMEM);
 	}
 
+	/*
+	 * Since frames remain on a queue after a return from xennet_start_xmit,
+	 * we can't support tx shared skbs
+	 */
+	netdev->priv_flags &= ~IFF_TX_SKB_SHARING;
+
 	np                   = netdev_priv(netdev);
 	np->xbdev            = dev;
 
-- 
1.7.6.4