Subject: Re: [PATCH net-next] net/core: generic support for disabling netdev features down stack

From: Alexander Duyck <[email-masked]>
Date: Mon, 2 Nov 2015 10:04:39 -0800

On 11/02/2015 09:53 AM, Jarod Wilson wrote:
> There are some netdev features, which when disabled on an upper device,
> such as a bonding master or a bridge, must be disabled and cannot be
> re-enabled on underlying devices.
>
> This is a rework of an earlier more heavy-handed appraoch, which simply
> disables and prevents re-enabling of netdev features listed in a new
> define in include/net/netdev_features.h, NETIF_F_UPPER_DISABLES. Any upper
> device that disables a flag in that feature mask, the disabling will
> propagate down the stack, and any lower device that has any upper device
> with one of those flags disabled should not be able to enable said flag.
>
> Initially, only LRO is included for proof of concept, and because this
> code effectively does the same thing as dev_disable_lro(), though it will
> also activate from the ethtool path, which was one of the goals here.
>
> [root@dell-per730-01 ~]# ethtool -k bond0 |grep large
> large-receive-offload: on
> [root@dell-per730-01 ~]# ethtool -k p5p1 |grep large
> large-receive-offload: on
> [root@dell-per730-01 ~]# ethtool -K bond0 lro off
> [root@dell-per730-01 ~]# ethtool -k bond0 |grep large
> large-receive-offload: off
> [root@dell-per730-01 ~]# ethtool -k p5p1 |grep large
> large-receive-offload: off
>
> dmesg dump:
>
> [ 1033.277986] bond0: Disabling feature 0x0000000000008000 on lower dev p5p2.
> [ 1034.067949] bnx2x 0000:06:00.1 p5p2: using MSI-X  IRQs: sp 74  fp[0] 76 ... fp[7] 83
> [ 1034.753612] bond0: Disabling feature 0x0000000000008000 on lower dev p5p1.
> [ 1035.591019] bnx2x 0000:06:00.0 p5p1: using MSI-X  IRQs: sp 62  fp[0] 64 ... fp[7] 71
>
> This has been successfully tested with bnx2x, qlcnic and netxen network
> cards as slaves in a bond interface. Turning LRO on or off on the master
> also turns it on or off on each of the slaves, new slaves are added with
> LRO in the same state as the master, and LRO can't be toggled on the
> slaves.
>
> Also, this should largely remove the need for dev_disable_lro(), and most,
> if not all, of its call sites can be replaced by simply making sure
> NETIF_F_LRO isn't included in the relevant device's feature flags.
>
> Note that this patch is driven by bug reports from users saying it was
> confusing that bonds and slaves had different settings for the same
> features, and while it won't be 100% in sync if a lower device doesn't
> support a feature like LRO, I think this is a good step in the right
> direction.
>
> CC: "David S. Miller" <[email-masked]>
> CC: Eric Dumazet <[email-masked]>
> CC: Jay Vosburgh <[email-masked]>
> CC: Veaceslav Falico <[email-masked]>
> CC: Andy Gospodarek <[email-masked]>
> CC: Jiri Pirko <[email-masked]>
> CC: Nikolay Aleksandrov <[email-masked]>
> CC: Michal Kubecek <[email-masked]>
> CC: Alexander Duyck <[email-masked]>
> CC: [email-masked]
> Signed-off-by: Jarod Wilson <[email-masked]>
> ---
> Note: this replaces "[RFC PATCH net-next] net/core: initial support for
> stacked dev feature toggles" for consideration.
>
>   include/linux/netdev_features.h | 11 +++++++++
>   net/core/dev.c                  | 52 +++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 63 insertions(+)
>
> diff --git a/include/linux/netdev_features.h b/include/linux/netdev_features.h
> index 9672781..0f5837a 100644
> --- a/include/linux/netdev_features.h
> +++ b/include/linux/netdev_features.h
> @@ -125,6 +125,11 @@ enum {
>   #define NETIF_F_HW_L2FW_DOFFLOAD	__NETIF_F(HW_L2FW_DOFFLOAD)
>   #define NETIF_F_BUSY_POLL	__NETIF_F(BUSY_POLL)
>
> +#define for_each_netdev_feature(mask_addr, feature)				\
> +	int bit;								\
> +	for_each_set_bit(bit, (unsigned long *)mask_addr, NETDEV_FEATURE_COUNT)	\
> +		feature = __NETIF_F_BIT(bit);
> +
>   /* Features valid for ethtool to change */
>   /* = all defined minus driver/device-class-related */
>   #define NETIF_F_NEVER_CHANGE	(NETIF_F_VLAN_CHALLENGED | \
> @@ -167,6 +172,12 @@ enum {
>    */
>   #define NETIF_F_ALL_FOR_ALL	(NETIF_F_NOCACHE_COPY | NETIF_F_FSO)
>
> +/*
> + * If upper/master device has these features disabled, they must be disabled
> + * on all lower/slave devices as well.
> + */
> +#define NETIF_F_UPPER_DISABLES	NETIF_F_LRO
> +
>   /* changeable features with no special hardware requirements */
>   #define NETIF_F_SOFT_FEATURES	(NETIF_F_GSO | NETIF_F_GRO)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 13f49f8..3a8dbbc 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -6288,9 +6288,51 @@ static void rollback_registered(struct net_device *dev)
>   	list_del(&single);
>   }
>
> +static netdev_features_t netdev_sync_upper_features(struct net_device *lower,
> +	struct net_device *upper, netdev_features_t features)
> +{
> +	netdev_features_t upper_disables = NETIF_F_UPPER_DISABLES;
> +	netdev_features_t feature;
> +
> +	for_each_netdev_feature(&upper_disables, feature) {
> +		if (!(upper->wanted_features & feature)
> +		    && (features & feature)) {
> +			netdev_dbg(lower, "Dropping feature %pNF, upper dev %s has it off.\n",
> +				   &feature, upper->name);
> +			features &= ~feature;
> +		}
> +	}
> +
> +	return features;
> +}
> +
> +static void netdev_sync_lower_features(struct net_device *upper,
> +	struct net_device *lower, netdev_features_t features)
> +{
> +	netdev_features_t upper_disables = NETIF_F_UPPER_DISABLES;
> +	netdev_features_t feature;
> +
> +	for_each_netdev_feature(&upper_disables, feature) {
> +		if (!(features & feature) && (lower->features & feature)) {
> +			netdev_dbg(upper, "Disabling feature %pNF on lower dev %s.\n",
> +				   &feature, lower->name);
> +			upper->wanted_features &= ~feature;

Isn't this line redundant? The upper device should have already cleared 
the bit from the wanted_features?  That is unless the ndo_fix_features 
call modified it in which case we shouldn't be modifying it ourselves.

> +			lower->wanted_features &= ~feature;
> +			netdev_update_features(lower);
> +
> +			if (unlikely(lower->features & feature))
> +				netdev_WARN(upper, "failed to disable %pNF on %s!\n",
> +					    &feature, lower->name);
> +		}
> +	}
> +}
> +
>   static netdev_features_t netdev_fix_features(struct net_device *dev,
>   	netdev_features_t features)
>   {
> +	struct net_device *upper, *lower;
> +	struct list_head *iter;
> +
>   	/* Fix illegal checksum combinations */
>   	if ((features & NETIF_F_HW_CSUM) &&
>   	    (features & (NETIF_F_IP_CSUM|NETIF_F_IPV6_CSUM))) {
> @@ -6345,6 +6387,16 @@ static netdev_features_t netdev_fix_features(struct net_device *dev,
>   		}
>   	}
>
> +	/* some features can't be enabled if they're off an an upper device */
> +	netdev_for_each_upper_dev_rcu(dev, upper, iter)
> +		features = netdev_sync_upper_features(dev, upper, features);
> +
> +	/* some features must be disabled on lower devices when disabled
> +	 * on an upper device (think: bonding master or bridge)
> +	 */
> +	netdev_for_each_lower_dev(dev, lower, iter)
> +		netdev_sync_lower_features(dev, lower, features);
> +

I don't know if this is the right spot for this.  You might want to look 
at placing this after the ndo_set_features call to handle things if 
there wasn't an error.  That way if a lower device for some reason has 
an issue with one of the other settings being changed you don't end up 
in a state where all the lower devices have the feature stripped while 
the upper device still reports it as being enabled.

>   #ifdef CONFIG_NET_RX_BUSY_POLL
>   	if (dev->netdev_ops->ndo_busy_poll)
>   		features |= NETIF_F_BUSY_POLL;
>