Re: [PATCH net-next 1/2] macvtap: Let TUNSETOFFLOAD actually controll offload features.

[Eric Dumazet <eric.dumazet@gmail.com>]

On Wed, 2013-06-19 at 10:47 -0400, Vlad Yasevich wrote:
> When the user issues TUNSETOFFLOAD ioctl, macvtap does not do
> anything other then to verify arguments.  This patch adds
> functionality to allow users to actually control offload features.
> NETIF_F_GSO and NETIF_F_GRO are always on, but the rest of the
> features can be controlled.
> 
> Signed-off-by: Vlad Yasevich <vyasevic@redhat.com>
> ---
>  drivers/net/macvlan.c      |  9 +++++++++
>  drivers/net/macvtap.c      | 41 ++++++++++++++++++++++++++++++++++++++++-
>  include/linux/if_macvlan.h |  1 +
>  3 files changed, 50 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c
> index edfddc5..fa47415 100644
> --- a/drivers/net/macvlan.c
> +++ b/drivers/net/macvlan.c
> @@ -638,6 +638,14 @@ static int macvlan_ethtool_get_settings(struct net_device *dev,
>  	return __ethtool_get_settings(vlan->lowerdev, cmd);
>  }
>  
> +static netdev_features_t macvlan_fix_features(struct net_device *dev,
> +					      netdev_features_t features)
> +{
> +	struct macvlan_dev *vlan = netdev_priv(dev);
> +
> +	return (features & vlan->set_features) | (features & ~MACVLAN_FEATURES);
> +}
> +
>  static const struct ethtool_ops macvlan_ethtool_ops = {
>  	.get_link		= ethtool_op_get_link,
>  	.get_settings		= macvlan_ethtool_get_settings,
> @@ -651,6 +659,7 @@ static const struct net_device_ops macvlan_netdev_ops = {
>  	.ndo_stop		= macvlan_stop,
>  	.ndo_start_xmit		= macvlan_start_xmit,
>  	.ndo_change_mtu		= macvlan_change_mtu,
> +	.ndo_fix_features	= macvlan_fix_features,
>  	.ndo_change_rx_flags	= macvlan_change_rx_flags,
>  	.ndo_set_mac_address	= macvlan_set_mac_address,
>  	.ndo_set_rx_mode	= macvlan_set_mac_lists,
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index 5a76f20..09f0b1f 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -976,6 +976,45 @@ static int macvtap_ioctl_set_queue(struct file *file, unsigned int flags)
>  	return ret;
>  }
>  
> +static int set_offload(struct macvtap_queue *q, unsigned long arg)
> +{
> +	struct macvlan_dev *vlan;
> +	netdev_features_t features = NETIF_F_GSO|NETIF_F_GRO;
> +	int err = 0;
> +
> +	if (arg & TUN_F_CSUM) {
> +		features = NETIF_F_HW_CSUM;
> +
> +		if (arg & (TUN_F_TSO4 | TUN_F_TSO6)) {
> +			if (arg & TUN_F_TSO_ECN)
> +				features |= NETIF_F_TSO_ECN;
> +			if (arg & TUN_F_TSO4)
> +				features |= NETIF_F_TSO;
> +			if (arg & TUN_F_TSO6)
> +				features |= NETIF_F_TSO6;
> +		}
> +
> +		if (arg & TUN_F_UFO)
> +			features |= NETIF_F_UFO;
> +	}
> +
> +	rtnl_lock();
> +	rcu_read_lock_bh();

This looks wrong/suspect to me.

Once RTNL is owned, you should not need rcu_read_lock_bh()

(A BH handler will not change q->vlan )

BTW, it looks like ->vlan is protected by macvtap_lock

> +	vlan = rcu_dereference_bh(q->vlan);

vlan = rtnl_dereference(q->vlan);

> +	if (!vlan) {
> +		err = -ENOLINK;
> +		goto unlock;
> +	}
> +
> +	vlan->set_features = features;
> +	netdev_update_features(vlan->dev);

Can this really be called with BH disabled ?

> +
> +unlock:
> +	rcu_read_unlock_bh();
> +	rtnl_unlock();
> +	return err;
> +}
> +