lkml.org 
[lkml]   [2020]   [Oct]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH net-next v2] net: dsa: Support bridge 802.1Q while untagging
From
Date


On 10/1/2020 4:24 PM, Vladimir Oltean wrote:
> On Wed, Sep 30, 2020 at 08:06:23PM -0700, Florian Fainelli wrote:
>> The intent of 412a1526d067 ("net: dsa: untag the bridge pvid from rx
>> skbs") is to transparently untag the bridge's default_pvid when the
>> Ethernet switch can only support egress tagged of that default_pvid
>> towards the CPU port.
>>
>> Prior to this commit, users would have to configure an 802.1Q upper on
>> the bridge master device when the bridge is configured with
>> vlan_filtering=0 in order to pop the VLAN tag:
>>
>> ip link add name br0 type bridge vlan_filtering 0
>> ip link add link br0 name br0.1 type vlan id 1
>>
>> After this commit we added support for managing a switch port 802.1Q
>> upper but those are not usually added as bridge members, and if they do,
>> they do not actually require any special management, the data path would
>> pop the desired VLAN tag accordingly.
>>
>> What we want to preserve is that use case and to manage when the user
>> creates that 802.1Q upper for the bridge port.
>>
>> While we are it, call __vlan_find_dev_deep_rcu() which makes use the
>> VLAN group array which is faster.
>>
>> As soon as we return the VLAN tagged SKB though it will be used by the
>> following call path:
>>
>> netif_receive_skb_list_internal
>> -> __netif_receive_skb_list_core
>> -> __netif_receive_skb_core
>> -> vlan_do_receive()
>>
>> which uses skb->vlan_proto, if we do not set it to the appropriate VLAN
>> protocol, we will leave it set to what the DSA master has set
>> (ETH_P_XDSA).
>>
>
> The explanation is super confusing, although I think the placement of
> the "skb->vlan_proto = vlan_dev_vlan_proto(upper_dev)" is correct.
> Here's what I think is going on. It has to do with what's upwards of the
> code you're changing:
>
> /* Move VLAN tag from data to hwaccel */
> if (!skb_vlan_tag_present(skb) && hdr->h_vlan_proto == htons(proto)) {
> skb = skb_vlan_untag(skb);
> if (!skb)
> return NULL;
> }
>
> So skb->vlan_proto should already be equal to the protocol of the 8021q
> upper, see the call path below.
>
> this is the problem
> |
> skb_vlan_untag() v
> -> __vlan_hwaccel_put_tag(skb, skb->protocol, vlan_tci);
> -> skb->vlan_proto = vlan_proto;

Ah, indeed!

>
> But the problem is that skb_vlan_untag() calls __vlan_hwaccel_put_tag
> with the wrong vlan_proto, it calls it with the skb->protocol which is
> still ETH_P_XDSA because we haven't re-run eth_type_trans() yet.
> It looks like this function wants pretty badly to be called after
> eth_type_trans(), and it's getting pretty messy because of that, but we
> don't have any other driver-specific hook afterwards..
>
> I don't have a lot of experience, the alternatives are either to:
> - move dsa_untag_bridge_pvid() after eth_type_trans(), similar to what
> you did in your initial patch - maybe this is the cleanest

This would be my preference and it would not be hurting the fast-path
that much.

> - make dsa_untag_bridge_pvid() call eth_type_trans() and this gets rid
> of the extra step you need to do in tag_brcm.c

Sure, however this requires that we remove the call to eth_type_trans()
in dsa_switch_rcv() or that we push/pull by an appropriate amount, not
very effective.

> - document this very well

I doubt this would survive the test of time unfortunately.

>
>> Fixes: 412a1526d067 ("net: dsa: untag the bridge pvid from rx skbs")
>> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
>> ---
>> Changes in v2:
>>
>> - removed unused list_head iter argument
>>
>> net/dsa/dsa_priv.h | 11 ++++-------
>> 1 file changed, 4 insertions(+), 7 deletions(-)
>>
>> diff --git a/net/dsa/dsa_priv.h b/net/dsa/dsa_priv.h
>> index 0348dbab4131..b4aafb2e90fa 100644
>> --- a/net/dsa/dsa_priv.h
>> +++ b/net/dsa/dsa_priv.h
>> @@ -205,7 +205,6 @@ static inline struct sk_buff *dsa_untag_bridge_pvid(struct sk_buff *skb)
>> struct net_device *br = dp->bridge_dev;
>> struct net_device *dev = skb->dev;
>> struct net_device *upper_dev;
>> - struct list_head *iter;
>> u16 vid, pvid, proto;
>> int err;
>>
>> @@ -247,12 +246,10 @@ static inline struct sk_buff *dsa_untag_bridge_pvid(struct sk_buff *skb)
>> * supports because vlan_filtering is 0. In that case, we should
>> * definitely keep the tag, to make sure it keeps working.
>> */
>> - netdev_for_each_upper_dev_rcu(dev, upper_dev, iter) {
>> - if (!is_vlan_dev(upper_dev))
>> - continue;
>> -
>> - if (vid == vlan_dev_vlan_id(upper_dev))
>> - return skb;
>> + upper_dev = __vlan_find_dev_deep_rcu(br, htons(proto), vid);
>> + if (upper_dev) {
>> + skb->vlan_proto = vlan_dev_vlan_proto(upper_dev);
>> + return skb;
>> }
>>
>> __vlan_hwaccel_clear_tag(skb);
>> --
>> 2.25.1

--
Florian

\
 
 \ /
  Last update: 2020-10-02 01:49    [W:0.064 / U:0.288 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site