netdev - Re: [PATCH net] net: sched: fix race condition in qdisc

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Date:   Sun, 20 Nov 2022 18:43:35 +0200
From:   Gal Pressman <gal@...dia.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Maxim Mikityanskiy <maximmi@...dia.com>,
        "David S . Miller" <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        Cong Wang <xiyou.wangcong@...il.com>, eric.dumazet@...il.com,
        syzbot <syzkaller@...glegroups.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Tariq Toukan <tariqt@...dia.com>,
        Maxim Mikityanskiy <maxtram95@...il.com>
Subject: Re: [PATCH net] net: sched: fix race condition in qdisc_graft()

On 20/11/2022 18:09, Eric Dumazet wrote:
> On Sat, Nov 19, 2022 at 11:42 PM Gal Pressman <gal@...dia.com> wrote:
>> On 10/11/2022 11:08, Gal Pressman wrote:
>>> On 06/11/2022 10:07, Gal Pressman wrote:
>>>> It reproduces consistently:
>>>> ip link set dev eth2 up
>>>> ip addr add 194.237.173.123/16 dev eth2
>>>> tc qdisc add dev eth2 clsact
>>>> tc qdisc add dev eth2 root handle 1: htb default 1 offload
>>>> tc class add dev eth2 classid 1: parent root htb rate 18000mbit ceil
>>>> 22500.0mbit burst 450000kbit cburst 450000kbit
>>>> tc class add dev eth2 classid 1:3 parent 1: htb rate 3596mbit burst
>>>> 89900kbit cburst 89900kbit
>>>> tc qdisc delete dev eth2 clsact
>>>> tc qdisc delete dev eth2 root handle 1: htb default 1
>>>>
>>>> Please let me know if there's anything else you want me to check.
>>> Hi Eric, did you get a chance to take a look?
>> No response for quite a long time, Jakub, should I submit a revert?
> Sorry, I won't have time to look at this before maybe two weeks.

Thanks for the response, Eric.

> If you want to revert a patch which is correct, because some code
> assumes something wrong,

I am not convinced about the "code assumes something wrong" part, and
not sure what are the consequences of this WARN being triggered, are you?

> I will simply say this seems not good.

Arguable, it is not that clear that a fix that introduces another issue
is a good thing, particularly when we don't understand the severity of
the thing that got broken.

Two weeks gets us to the end of -rc7, a bit too dangerous to my personal
taste, but I'm not the one making the calls.