netdev - Re: [Intel-wired-lan] [RFC PATCH net] e1000e: keep vlan interfaces functional after rxvlan off

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Date:	Wed, 1 Jun 2016 15:31:46 -0700
From:	Alexander Duyck <alexander.duyck@...il.com>
To:	Jarod Wilson <jarod@...hat.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Netdev <netdev@...r.kernel.org>,
	intel-wired-lan <intel-wired-lan@...ts.osuosl.org>
Subject: Re: [Intel-wired-lan] [RFC PATCH net] e1000e: keep vlan interfaces
 functional after rxvlan off

On Wed, Jun 1, 2016 at 12:27 PM, Jarod Wilson <jarod@...hat.com> wrote:
> On Wed, Jun 01, 2016 at 07:31:53AM -0700, Alexander Duyck wrote:
>> On Tue, May 17, 2016 at 12:03 PM, Jarod Wilson <jarod@...hat.com> wrote:
>> > I've got a bug report about an e1000e interface, where a vlan interface is
>> > set up on top of it:
>> >
>> > $ ip link add link ens1f0 name ens1f0.99 type vlan id 99
>> > $ ip link set ens1f0 up
>> > $ ip link set ens1f0.99 up
>> > $ ip addr add 192.168.99.92 dev ens1f0.99
>> >
>> > At this point, I can ping another host on vlan 99, ip 192.168.99.91.
>> > However, if I do the following:
>> >
>> > $ ethtool -K ens1f0 rxvlan off
>> >
>> > Then no traffic passes on ens1f0.99. It comes back if I toggle rxvlan on
>> > again. I'm not sure if this is actually intended behavior, or if there's a
>> > lack of software vlan stripping fallback, or what, but things continue to
>> > work if I simply don't call e1000e_vlan_strip_disable() if there are
>> > active vlans (plagiarizing a function from the e1000 driver here) on the
>> > interface.
>> >
>> > Also slipped a related-ish fix to the kerneldoc text for
>> > e1000e_vlan_strip_disable here...
>> >
>> > CC: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
>> > CC: intel-wired-lan@...ts.osuosl.org
>> > CC: netdev@...r.kernel.org
>> > Signed-off-by: Jarod Wilson <jarod@...hat.com>
>> > ---
>> >  drivers/net/ethernet/intel/e1000e/netdev.c | 15 +++++++++++++--
>> >  1 file changed, 13 insertions(+), 2 deletions(-)
>> >
>> > diff --git a/drivers/net/ethernet/intel/e1000e/netdev.c b/drivers/net/ethernet/intel/e1000e/netdev.c
>> > index 75e6089..73f7452 100644
>> > --- a/drivers/net/ethernet/intel/e1000e/netdev.c
>> > +++ b/drivers/net/ethernet/intel/e1000e/netdev.c
>> > @@ -154,6 +154,16 @@ void __ew32(struct e1000_hw *hw, unsigned long reg, u32 val)
>> >         writel(val, hw->hw_addr + reg);
>> >  }
>> >
>> > +static bool e1000e_vlan_used(struct e1000_adapter *adapter)
>> > +{
>> > +       u16 vid;
>> > +
>> > +       for_each_set_bit(vid, adapter->active_vlans, VLAN_N_VID)
>> > +               return true;
>> > +
>>
>> I'm pretty sure this is always going to return true if 8021q is loaded
>> because VLAN 0 is always added to the device even if no other VLANs
>> are in use.
>
> Ah, hadn't considered that, I just plucked it straight from e1000.
>
>> > +       return false;
>> > +}
>> > +
>> >  /**
>> >   * e1000_regdump - register printout routine
>> >   * @hw: pointer to the HW structure
>> > @@ -2789,7 +2799,7 @@ static void e1000e_vlan_filter_enable(struct e1000_adapter *adapter)
>> >  }
>> >
>> >  /**
>> > - * e1000e_vlan_strip_enable - helper to disable HW VLAN stripping
>> > + * e1000e_vlan_strip_disable - helper to disable HW VLAN stripping
>> >   * @adapter: board private structure to initialize
>> >   **/
>> >  static void e1000e_vlan_strip_disable(struct e1000_adapter *adapter)
>> > @@ -3443,7 +3453,8 @@ static void e1000e_set_rx_mode(struct net_device *netdev)
>> >
>> >         ew32(RCTL, rctl);
>> >
>> > -       if (netdev->features & NETIF_F_HW_VLAN_CTAG_RX)
>> > +       if (netdev->features & NETIF_F_HW_VLAN_CTAG_RX ||
>> > +           e1000e_vlan_used(adapter))
>> >                 e1000e_vlan_strip_enable(adapter);
>> >         else
>> >                 e1000e_vlan_strip_disable(adapter);
>>
>> So if the VLAN tag stripping is disabled what happens that is causing
>> the VLAN test to fail?  It sounds like this might be working around a
>> kernel bug where a VLAN created on a device that supports hardware tag
>> stripping only supports hardware tag stripping.  Maybe a better fix
>> would be to add a fall back so if the VLAN tag is in the frame instead
>> of stripped it still makes it to the correct spot.
>
> That's the main reason I labeled it as an RFC -- I wasn't sure exactly how
> things were intended to work when the hardware stripping was disabled. It
> seems quite plausible to me that this patch simply papers over the real
> bug: lack of a functional software fallback. I'm not particularly up on
> the vlan code just yet though, so I'm not yet sure where to poke next.
> Suggestions welcomed. :)

Well the software fallback should be the call to skb_vlan_untag in
__netif_receive_skb_core.  If that isn't being triggered then we
should probably be fixing the files in the core code then.

- Alex