netdev - Re: [PATCH v2 net 2/2] net: core: generic XDP support for stacked device

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Date:   Tue, 21 May 2019 12:47:23 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Jiri Pirko <jiri@...nulli.us>,
        Stephen Hemminger <stephen@...workplumber.org>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        xdp-newbies@...r.kernel.org, bpf@...r.kernel.org,
        Stephen Hemminger <sthemmin@...rosoft.com>
Subject: Re: [PATCH v2 net 2/2] net: core: generic XDP support for stacked
 device


On 2019/5/20 下午5:11, Jiri Pirko wrote:
> Sun, May 19, 2019 at 05:10:46AM CEST, stephen@...workplumber.org wrote:
>> When a device is stacked like (team, bonding, failsafe or netvsc) the
>> XDP generic program for the parent device is not called.  In these
>> cases, the rx handler changes skb->dev to its own in the receive
>> handler, and returns RX_HANDLER_ANOTHER.  Fix this by calling
>> do_xdp_generic if necessary before starting another round.
>>
>> Review of all the places RX_HANDLER_ANOTHER is returned
>> show that the current devices do correctly change skb->dev.
>>
>> There was an older patch that got abandoned that did the
>> same thing, this is just a rewrite.
>>
>> Suggested-by: Jason Wang <jasowang@...hat.com>
>> Fixes: d445516966dc ("net: xdp: support xdp generic on virtual devices")
>> Signed-off-by: Stephen Hemminger <sthemmin@...rosoft.com>
>> Acked-by: Jason Wang <jasowang@...hat.com>
>> ---
>> net/core/dev.c | 10 ++++++++++
>> 1 file changed, 10 insertions(+)
>>
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index b6b8505cfb3e..240d0b2de1a8 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -4921,6 +4921,16 @@ static int __netif_receive_skb_core(struct sk_buff *skb, bool pfmemalloc,
>> 			ret = NET_RX_SUCCESS;
>> 			goto out;
>> 		case RX_HANDLER_ANOTHER:
>> +			if (static_branch_unlikely(&generic_xdp_needed_key)) {
>> +				struct bpf_prog *xdp_prog;
>> +
>> +				xdp_prog = rcu_dereference(skb->dev->xdp_prog);
>> +				ret = do_xdp_generic(xdp_prog, skb);
>> +				if (ret != XDP_PASS) {
>> +					ret = NET_RX_SUCCESS;
>> +					goto out;
>> +				}
>> +			}
> I'm always scarred of changes like this. The history tells us that this
> codepaths are very fragile. It took us non-trivial efford to fix bonding
> here, not to mention vlans (that was pain).


I may miss something, did you see any issue for bonding with this patch?


>
> The reason for troubles was often fact that different flows were treated
> differently (vlan accel/non-accel).


Do you mean we need do something similar after vlan_do_receive() returns 
true?


> This patch calls do_xdp_generic for master device in different point in
> the receive patch comparing to lower device. Would it be possible to
> unify this? E.g. by moving do_xdp_generice() call from
> netif_rx_internal()/netif_receive_skb_internal() here,
> to the beginning of __netif_receive_skb_core()?


Probably just after another_round label. And this means generic XDP is 
done after RPS which could be even better.

Thanks


>
>
>
>> 			goto another_round;
>> 		case RX_HANDLER_EXACT:
>> 			deliver_exact = true;
>> -- 
>> 2.20.1
>>