linux-kernel - Re: [PATCH v2 net] net: sch_generic: aviod concurrent reset and enqueue op for lockless qdisc

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Message-ID: <CAM_iQpX0XzNDCzc2U5=g6aU-HGYs3oryHx=rmM3ue9sH=Jd4Gw@mail.gmail.com>
Date:   Wed, 28 Oct 2020 10:47:30 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     "Pai, Vishwanath" <vpai@...mai.com>
Cc:     Yunsheng Lin <linyunsheng@...wei.com>,
        "Hunt, Joshua" <johunt@...mai.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "linuxarm@...wei.com" <linuxarm@...wei.com>,
        John Fastabend <john.fastabend@...il.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH v2 net] net: sch_generic: aviod concurrent reset and
 enqueue op for lockless qdisc

On Wed, Oct 28, 2020 at 8:37 AM Pai, Vishwanath <vpai@...mai.com> wrote:
> Hi,
>
> We noticed some problems when testing the latest 5.4 LTS kernel and traced it
> back to this commit using git bisect. When running our tests the machine stops
> responding to all traffic and the only way to recover is a reboot. I do not see
> a stack trace on the console.

Do you mean the machine is still running fine just the network is down?

If so, can you dump your tc config with stats when the problem is happening?
(You can use `tc -s -d qd show ...`.)

>
> This can be reproduced using the packetdrill test below, it should be run a
> few times or in a loop. You should hit this issue within a few tries but
> sometimes might take up to 15-20 tries.
...
> I can reproduce the issue easily on v5.4.68, and after reverting this commit it
> does not happen anymore.

This is odd. The patch in this thread touches netdev reset path, if packetdrill
is the only thing you use to trigger the bug (that is netdev is always active),
I can not connect them.

Thanks.