netdev - Re: Packet gets stuck in NOLOCK pfifo

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Message-ID: <CAM_iQpU+YD9AcX_77kqmQkqKMuOtnRh5xoGcz9dRRJTe1OnpBQ@mail.gmail.com>
Date:   Mon, 5 Apr 2021 18:49:58 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Jiri Kosina <jikos@...nel.org>
Cc:     Hillf Danton <hdanton@...a.com>,
        John Fastabend <john.fastabend@...il.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Kehuan Feng <kehuan.feng@...il.com>,
        Jike Song <albcamus@...il.com>,
        Jonas Bonn <jonas.bonn@...rounds.com>,
        Michael Zhivich <mzhivich@...mai.com>,
        David Miller <davem@...emloft.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Kubecek <mkubecek@...e.cz>,
        Netdev <netdev@...r.kernel.org>, Josh Hunt <johunt@...mai.com>,
        Yunsheng Lin <linyunsheng@...wei.com>
Subject: Re: Packet gets stuck in NOLOCK pfifo_fast qdisc

On Sat, Apr 3, 2021 at 5:23 AM Jiri Kosina <jikos@...nel.org> wrote:
>
> I am still planning to have Yunsheng Lin's (CCing) fix [1] tested in the
> coming days. If it works, then we can consider proceeding with it,
> otherwise I am all for reverting the whole NOLOCK stuff.
>
> [1] https://lore.kernel.org/linux-can/1616641991-14847-1-git-send-email-linyunsheng@huawei.com/T/#u

I personally prefer to just revert that bit, as it brings more troubles
than gains. Even with Yunsheng's patch, there are still some issues.
Essentially, I think the core qdisc scheduling code is not ready for
lockless, just look at those NOLOCK checks in sch_generic.c. :-/

Thanks.