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

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Message-ID: <20190521060853.GA2210@nanopsycho.orion>
Date:   Tue, 21 May 2019 08:08:53 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        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

Tue, May 21, 2019 at 06:47:23AM CEST, jasowang@...hat.com wrote:
>
>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?

No, I was talking about past.


>
>
>> 
>> 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?

No.


>
>
>> 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.

Yes. That is exactly the place I have in mind.


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