Messages in this thread | | | Subject | Re: [PATCH net-next v2] net: dsa: Support bridge 802.1Q while untagging | From | Florian Fainelli <> | Date | Thu, 1 Oct 2020 16:48:43 -0700 |
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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
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