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From: Michal Kubecek <mkubecek@suse.cz>
To: Yunsheng Lin <linyunsheng@huawei.com>
Cc: Jiri Kosina <jikos@kernel.org>, Hillf Danton <hdanton@sina.com>,
	John Fastabend <john.fastabend@gmail.com>,
	Cong Wang <xiyou.wangcong@gmail.com>,
	Paolo Abeni <pabeni@redhat.com>,
	Kehuan Feng <kehuan.feng@gmail.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>,
	Netdev <netdev@vger.kernel.org>, Josh Hunt <johunt@akamai.com>
Subject: Re: Packet gets stuck in NOLOCK pfifo_fast qdisc
Date: Tue, 6 Apr 2021 09:06:59 +0200	[thread overview]
Message-ID: <20210406070659.t6csfgkskbmmxtx5@lion.mk-sys.cz> (raw)
In-Reply-To: <eaff25bc-9b64-037e-b9bc-c06fc4a5a9fb@huawei.com>

On Tue, Apr 06, 2021 at 08:55:41AM +0800, Yunsheng Lin wrote:
> 
> Hi, Jiri
> Do you have a reproducer that can be shared here?
> With reproducer, I can debug and test it myself too.

I'm afraid we are not aware of a simple reproducer. As mentioned in the
original discussion, the race window is extremely small and the other
thread has to do quite a lot in the meantime which is probably why, as
far as I know, this was never observed on real hardware, only in
virtualization environments. NFS may also be important as, IIUC, it can
often issue an RPC request from a different CPU right after a data
transfer. Perhaps you could cheat a bit and insert a random delay
between the empty queue check and releasing q->seqlock to make it more
likely to happen.

Other than that, it's rather just "run this complex software in a xen VM
and wait".

Michal

  reply	other threads:[~2021-04-06  7:07 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
     [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 [this message]
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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