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

From: Jarod Wilson <[email-masked]>
Date: Mon, 02 Nov 2015 16:57:39 -0500

Alexander Duyck wrote:
> 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.

With the upper/lower feature sync calls where they currently are, no, 
its actually necessary to prevent flip-flopping flag values.

...
>> @@ -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.

I'll give it a go after the .ndo_set_features calls in 
__netdev_update_features(), see what shakes loose. Might even not need 
the extra upper->wanted_features twiddling with it here.

-- 
Jarod Wilson
[email-masked]