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Message-ID: <Yzig5mvDDFqqieDl@pop-os.localdomain> Date: Sat, 1 Oct 2022 13:19:50 -0700 From: Cong Wang <xiyou.wangcong@...il.com> To: Paul Blakey <paulb@...dia.com> Cc: Daniel Borkmann <daniel@...earbox.net>, Vlad Buslov <vladbu@...dia.com>, Oz Shlomo <ozsh@...dia.com>, Roi Dayan <roid@...dia.com>, netdev@...r.kernel.org, Saeed Mahameed <saeedm@...dia.com>, Eric Dumazet <edumazet@...gle.com>, "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com> Subject: Re: [PATCH net v2 1/2] net: Fix return value of qdisc ingress handling on success On Wed, Sep 28, 2022 at 10:55:49AM +0300, Paul Blakey wrote: > > > On 25/09/2022 21:00, Cong Wang wrote: > > On Sun, Sep 25, 2022 at 11:14:21AM +0300, Paul Blakey wrote: > > > Currently qdisc ingress handling (sch_handle_ingress()) doesn't > > > set a return value and it is left to the old return value of > > > the caller (__netif_receive_skb_core()) which is RX drop, so if > > > the packet is consumed, caller will stop and return this value > > > as if the packet was dropped. > > > > > > This causes a problem in the kernel tcp stack when having a > > > egress tc rule forwarding to a ingress tc rule. > > > The tcp stack sending packets on the device having the egress rule > > > will see the packets as not successfully transmitted (although they > > > actually were), will not advance it's internal state of sent data, > > > and packets returning on such tcp stream will be dropped by the tcp > > > stack with reason ack-of-unsent-data. See reproduction in [0] below. > > > > > > > Hm, but how is this return value propagated to egress? I checked > > tcf_mirred_act() code, but don't see how it is even used there. > > > > 318 err = tcf_mirred_forward(want_ingress, skb2); > > 319 if (err) { > > 320 out: > > 321 tcf_action_inc_overlimit_qstats(&m->common); > > 322 if (tcf_mirred_is_act_redirect(m_eaction)) > > 323 retval = TC_ACT_SHOT; > > 324 } > > 325 __this_cpu_dec(mirred_rec_level); > > 326 > > 327 return retval; > > > > > > What am I missing? > > for the ingress acting act_mirred it will return TC_ACT_CONSUMED above > the code you mentioned (since redirect=1, use_reinsert=1. Although > TC_ACT_STOLEN which is the retval set for this action, will also act the > same) > > > It is propagated as such (TX stack starting from tcp): > Sorry for my misunderstanding. I meant to say those TC_ACT_* return value, not NET_RX_*, but I worried too much here, as mirred lets user specify the return value. BTW, it seems you at least miss the drop case, which is NET_RX_DROP for TC_ACT_SHOT at least? Possibly other code paths in sch_handle_ingress() too. Thanks.
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