From: Josh Hunt <johunt@akamai.com>
To: Jiri Kosina <jikos@kernel.org>,
John Fastabend <john.fastabend@gmail.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>,
Paolo Abeni <pabeni@redhat.com>,
Kehuan Feng <kehuan.feng@gmail.com>,
Hillf Danton <hdanton@sina.com>, Jike Song <albcamus@gmail.com>,
Jonas Bonn <jonas.bonn@netrounds.com>,
Michael Zhivich <mzhivich@akamai.com>,
David Miller <davem@davemloft.net>,
LKML <linux-kernel@vger.kernel.org>,
Michal Kubecek <mkubecek@suse.cz>,
Netdev <netdev@vger.kernel.org>
Subject: Re: Packet gets stuck in NOLOCK pfifo_fast qdisc
Date: Fri, 2 Apr 2021 12:33:38 -0700 [thread overview]
Message-ID: <39c837d3-0435-a5a7-ac48-975a4d2f170e@akamai.com> (raw)
In-Reply-To: <nycvar.YFH.7.76.2104022120050.12405@cbobk.fhfr.pm>
On 4/2/21 12:25 PM, Jiri Kosina wrote:
> On Thu, 3 Sep 2020, John Fastabend wrote:
>
>>>> At this point I fear we could consider reverting the NOLOCK stuff.
>>>> I personally would hate doing so, but it looks like NOLOCK benefits are
>>>> outweighed by its issues.
>>>
>>> I agree, NOLOCK brings more pains than gains. There are many race
>>> conditions hidden in generic qdisc layer, another one is enqueue vs.
>>> reset which is being discussed in another thread.
>>
>> Sure. Seems they crept in over time. I had some plans to write a
>> lockless HTB implementation. But with fq+EDT with BPF it seems that
>> it is no longer needed, we have a more generic/better solution. So
>> I dropped it. Also most folks should really be using fq, fq_codel,
>> etc. by default anyways. Using pfifo_fast alone is not ideal IMO.
>
> Half a year later, we still have the NOLOCK implementation
> present, and pfifo_fast still does set the TCQ_F_NOLOCK flag on itself.
>
> And we've just been bitten by this very same race which appears to be
> still unfixed, with single packet being stuck in pfifo_fast qdisc
> basically indefinitely due to this very race that this whole thread began
> with back in 2019.
>
> Unless there are
>
> (a) any nice ideas how to solve this in an elegant way without
> (re-)introducing extra spinlock (Cong's fix) or
>
> (b) any objections to revert as per the argumentation above
>
> I'll be happy to send a revert of the whole NOLOCK implementation next
> week.
>
Jiri
If you have a reproducer can you try
https://lkml.org/lkml/2021/3/24/1485 ? If that doesn't work I think your
suggestion of reverting nolock makes sense to me. We've moved to using
fq as our default now b/c of this bug.
Josh
next prev parent reply other threads:[~2021-04-02 19:33 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-09 6:46 Packet gets stuck in NOLOCK pfifo_fast qdisc Jonas Bonn
2019-10-09 19:14 ` Paolo Abeni
2019-10-10 6:27 ` Jonas Bonn
2019-10-11 0:39 ` Jonas Bonn
2020-06-23 13:42 ` Michael Zhivich
2020-06-30 19:14 ` Josh Hunt
2020-07-01 7:53 ` Jonas Bonn
2020-07-01 16:05 ` Cong Wang
2020-07-01 19:58 ` Cong Wang
2020-07-01 22:02 ` Josh Hunt
2020-07-02 6:14 ` Jonas Bonn
2020-07-02 9:45 ` Paolo Abeni
2020-07-02 18:08 ` Josh Hunt
2020-07-07 14:18 ` Paolo Abeni
2020-07-08 20:16 ` Cong Wang
2020-07-09 9:20 ` Paolo Abeni
2020-07-08 20:33 ` Zhivich, Michael
2020-08-20 7:43 ` Jike Song
2020-08-20 18:13 ` Josh Hunt
[not found] ` <20200822032800.16296-1-hdanton@sina.com>
2020-08-25 2:18 ` Fengkehuan Feng
[not found] ` <20200825032312.11776-1-hdanton@sina.com>
2020-08-25 7:14 ` Fengkehuan Feng
[not found] ` <20200825162329.11292-1-hdanton@sina.com>
2020-08-26 2:38 ` Kehuan Feng
[not found] ` <CACS=qqKptAQQGiMoCs1Zgs9S4ZppHhasy1AK4df2NxnCDR+vCw@mail.gmail.com>
[not found] ` <5f46032e.1c69fb81.9880c.7a6cSMTPIN_ADDED_MISSING@mx.google.com>
2020-08-27 6:56 ` Kehuan Feng
[not found] ` <20200827125747.5816-1-hdanton@sina.com>
2020-08-28 1:45 ` Kehuan Feng
2020-09-03 5:01 ` Cong Wang
2020-09-03 8:39 ` Paolo Abeni
2020-09-03 17:43 ` Cong Wang
2020-09-04 5:07 ` John Fastabend
2020-09-10 20:15 ` Cong Wang
2020-09-10 21:07 ` John Fastabend
2020-09-10 21:40 ` Paolo Abeni
2021-04-02 19:25 ` Jiri Kosina
2021-04-02 19:33 ` Josh Hunt [this message]
[not found] ` <20210403003537.2032-1-hdanton@sina.com>
2021-04-03 12:23 ` Jiri Kosina
2021-04-06 0:55 ` Yunsheng Lin
2021-04-06 7:06 ` Michal Kubecek
2021-04-06 10:13 ` Juergen Gross
2021-04-06 12:17 ` Yunsheng Lin
2021-04-06 1:49 ` Cong Wang
2021-04-06 2:46 ` Yunsheng Lin
2021-04-06 7:31 ` Michal Kubecek
2021-04-06 12:24 ` Yunsheng Lin
[not found] ` <20200903101957.428-1-hdanton@sina.com>
2020-09-04 3:20 ` Kehuan Feng
2020-09-10 20:19 ` Cong Wang
2020-09-14 2:10 ` Yunsheng Lin
2020-09-17 19:52 ` Cong Wang
2020-09-18 2:06 ` Kehuan Feng
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