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Date: Sat, 1 Oct 2022 13:33:19 -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 Sat, Oct 01, 2022 at 01:19:50PM -0700, Cong Wang wrote: > 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. > I mean: diff --git a/net/core/dev.c b/net/core/dev.c index fa53830d0683..d1db8210d671 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -5109,6 +5109,7 @@ sch_handle_ingress(struct sk_buff *skb, struct packet_type **pt_prev, int *ret, struct mini_Qdisc *miniq = rcu_dereference_bh(skb->dev->miniq_ingress); struct tcf_result cl_res; + *ret = NET_RX_SUCCESS; /* If there's at least one ingress present somewhere (so * we get here via enabled static key), remaining devices * that are not configured with an ingress qdisc will bail @@ -5136,6 +5137,7 @@ sch_handle_ingress(struct sk_buff *skb, struct packet_type **pt_prev, int *ret, case TC_ACT_SHOT: mini_qdisc_qstats_cpu_drop(miniq); kfree_skb_reason(skb, SKB_DROP_REASON_TC_INGRESS); + *ret = NET_RX_DROP; return NULL; case TC_ACT_STOLEN: case TC_ACT_QUEUED: @@ -5160,6 +5162,7 @@ sch_handle_ingress(struct sk_buff *skb, struct packet_type **pt_prev, int *ret, break; } #endif /* CONFIG_NET_CLS_ACT */ + *ret = NET_RX_SUCCESS; return skb; }
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