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Message-ID: <20230511162023.3651970b@kernel.org>
Date: Thu, 11 May 2023 16:20:23 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Peilin Ye <yepeilin.cs@...il.com>, Jiri Pirko <jiri@...nulli.us>,
Daniel Borkmann <daniel@...earbox.net>
Cc: "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Paolo Abeni <pabeni@...hat.com>,
Jamal Hadi Salim <jhs@...atatu.com>,
Cong Wang <xiyou.wangcong@...il.com>,
Peilin Ye <peilin.ye@...edance.com>,
John Fastabend <john.fastabend@...il.com>,
Vlad Buslov <vladbu@...lanox.com>,
Pedro Tammela <pctammela@...atatu.com>,
Hillf Danton <hdanton@...a.com>, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, Cong Wang <cong.wang@...edance.com>
Subject: Re: [PATCH net 6/6] net/sched: qdisc_destroy() old ingress and
clsact Qdiscs before grafting
On Thu, 11 May 2023 13:40:10 -0700 Peilin Ye wrote:
> On Wed, May 10, 2023 at 04:15:59PM -0700, Jakub Kicinski wrote:
> > My thinking was to make sure that dev->miniq_* pointers always point
> > to one of the miniqs of the currently attached qdisc. Right now, on
> > a quick look, those pointers are not initialized during initial graft,
> > only when first filter is added, and may be cleared when filters are
> > removed. But I don't think that's strictly required, miniq with no
> > filters should be fine.
>
> Ah, I see, thanks for explaining, I didn't think of that. Looking at
> sch_handle_ingress() BTW, currently mini Qdisc stats aren't being updated
> (mini_qdisc_bstats_cpu_update()) if there's no filters, is this intended?
> Should I keep this behavior by:
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 735096d42c1d..9016481377e0 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -5116,7 +5116,7 @@ sch_handle_ingress(struct sk_buff *skb, struct packet_type **pt_prev, int *ret,
> * that are not configured with an ingress qdisc will bail
> * out here.
> */
> - if (!miniq)
> + if (!miniq || !miniq->filter_list)
> return skb;
>
> if (*pt_prev) {
Good question, maybe Jiri or Daniel can answer?
> On Wed, May 10, 2023 at 04:15:59PM -0700, Jakub Kicinski wrote:
> > On Wed, 10 May 2023 13:11:19 -0700 Peilin Ye wrote:
> > > Looking at the code, I think there is no guarantee that (1st) cannot
> > > happen after (2nd), although unlikely? Can RTNL-lockless RTM_NEWTFILTER
> > > handlers get preempted?
> >
> > Right, we need qdisc_graft(B) to update the appropriate dev pointer
> > to point to b1. With that the ordering should not matter. Probably
> > using the ->attach() callback?
>
> ->attach() is later than dev_graft_qdisc(). We should get ready for
> concurrent filter requests (i.e. have dev pointer pointing to b1) before
> grafting (publishing) B.
I thought even for "unlocked" filter operations the start of it is
under the lock, but the lock gets dropped after qdisc/block are found.
I could be misremembering, I haven't looked at the code.
> Also currently qdisc_graft() doesn't call
> ->attach() for ingress and clsact Qdiscs.
>
> But I see your point, thanks for the suggestion! I'll try ->init() and
> create v2.
->init() may be too early, aren't there any error points which could
prevent the Qdisc from binding after ->init() was called?
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