netdev - Re: Packet gets stuck in NOLOCK pfifo

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Date:   Thu, 10 Sep 2020 13:15:14 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     Paolo Abeni <pabeni@...hat.com>,
        Kehuan Feng <kehuan.feng@...il.com>,
        Hillf Danton <hdanton@...a.com>,
        Jike Song <albcamus@...il.com>, Josh Hunt <johunt@...mai.com>,
        Jonas Bonn <jonas.bonn@...rounds.com>,
        Michael Zhivich <mzhivich@...mai.com>,
        David Miller <davem@...emloft.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>
Subject: Re: Packet gets stuck in NOLOCK pfifo_fast qdisc

On Thu, Sep 3, 2020 at 10:08 PM John Fastabend <john.fastabend@...il.com> wrote:
> Maybe this would unlock us,
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 7df6c9617321..9b09429103f1 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -3749,7 +3749,7 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
>
>         if (q->flags & TCQ_F_NOLOCK) {
>                 rc = q->enqueue(skb, q, &to_free) & NET_XMIT_MASK;
> -               qdisc_run(q);
> +               __qdisc_run(q);
>
>                 if (unlikely(to_free))
>                         kfree_skb_list(to_free);
>
>
> Per other thread we also need the state deactivated check added
> back.

I guess no, because pfifo_dequeue() seems to require q->seqlock,
according to comments in qdisc_run(), so we can not just get rid of
qdisc_run_begin()/qdisc_run_end() here.

Thanks.