From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 35A88C33CA2 for ; Sun, 12 Jan 2020 21:29:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EB90E2187F for ; Sun, 12 Jan 2020 21:29:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387422AbgALV3U (ORCPT ); Sun, 12 Jan 2020 16:29:20 -0500 Received: from metis.ext.pengutronix.de ([85.220.165.71]:42675 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732914AbgALV3T (ORCPT ); Sun, 12 Jan 2020 16:29:19 -0500 Received: from gallifrey.ext.pengutronix.de ([2001:67c:670:201:5054:ff:fe8d:eefb] helo=[IPv6:::1]) by metis.ext.pengutronix.de with esmtp (Exim 4.92) (envelope-from ) id 1iqknO-0003Lx-11; Sun, 12 Jan 2020 22:29:18 +0100 Subject: Re: [BUG] pfifo_fast may cause out-of-order CAN frame transmission To: Paolo Abeni , linux-can@vger.kernel.org, netdev@vger.kernel.org Cc: kernel@pengutronix.de References: <661cc33a-5f65-2769-cc1a-65791cb4b131@pengutronix.de> <7717e4470f6881bbc92645c72ad7f6ec71360796.camel@redhat.com> <779d3346-0344-9064-15d5-4d565647a556@pengutronix.de> <1b70f56b72943bf5dfd2813565373e8c1b639c31.camel@redhat.com> From: Ahmad Fatoum Message-ID: <53ce1ab4-3346-2367-8aa5-85a89f6897ec@pengutronix.de> Date: Sun, 12 Jan 2020 22:29:17 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: <1b70f56b72943bf5dfd2813565373e8c1b639c31.camel@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 2001:67c:670:201:5054:ff:fe8d:eefb X-SA-Exim-Mail-From: a.fatoum@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: netdev@vger.kernel.org Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Hello Paolo, On 1/10/20 5:31 PM, Paolo Abeni wrote: > On Thu, 2020-01-09 at 18:39 +0100, Ahmad Fatoum wrote: >> Hello Paolo, >> >> On 1/9/20 1:51 PM, Paolo Abeni wrote: >>> On Wed, 2020-01-08 at 15:55 +0100, Ahmad Fatoum wrote: >>>> I've run into an issue of CAN frames being sent out-of-order on an i.MX6 Dual >>>> with Linux v5.5-rc5. Bisecting has lead me down to this commit: >>> >>> Thank you for the report. >> >> Thanks for the prompt patch. :-) >> >>> The code is only build-tested, could you please try it in your setup? >> >> Issue still persists, albeit appears to have become much less frequent. Took 2 million >> frames till first two were swapped. What I usually saw was a swap every few thousand >> frames at least and quite often more frequent than that. Might just be noise though. > > Thank you for testing. Even with the proposed patch there is still a > possible race condition: the CPU holding the seqlock can clear the > 'empty' flag after that the CPU xmitting the packet enqueue it and set > the 'empty' flag. > > The only option I can think of - beyond plain revert - is updating the > 'empty' flag in a even a more coarse way, as in the following patch. > > Again, the code only build tested and very rough, but it would be > helpful if you could give it a spin. Issue still reproducible despite the new patch. Thanks Ahmad > > Thank you! > > Paolo > > --- > diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h > index 6a70845bd9ab..fb365fbf65f8 100644 > --- a/include/net/pkt_sched.h > +++ b/include/net/pkt_sched.h > @@ -113,7 +113,7 @@ bool sch_direct_xmit(struct sk_buff *skb, struct Qdisc *q, > struct net_device *dev, struct netdev_queue *txq, > spinlock_t *root_lock, bool validate); > > -void __qdisc_run(struct Qdisc *q); > +int __qdisc_run(struct Qdisc *q); > > static inline void qdisc_run(struct Qdisc *q) > { > diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h > index fceddf89592a..df460fe0773a 100644 > --- a/include/net/sch_generic.h > +++ b/include/net/sch_generic.h > @@ -158,7 +158,6 @@ static inline bool qdisc_run_begin(struct Qdisc *qdisc) > if (qdisc->flags & TCQ_F_NOLOCK) { > if (!spin_trylock(&qdisc->seqlock)) > return false; > - WRITE_ONCE(qdisc->empty, false); > } else if (qdisc_is_running(qdisc)) { > return false; > } > diff --git a/net/core/dev.c b/net/core/dev.c > index 0ad39c87b7fd..b6378bb7b64a 100644 > --- a/net/core/dev.c > +++ b/net/core/dev.c > @@ -3624,10 +3624,22 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q, > end_run: > qdisc_run_end(q); > } else { > + int quota = 0; > + > rc = q->enqueue(skb, q, &to_free) & NET_XMIT_MASK; > - qdisc_run(q); > + if (!qdisc_run_begin(q)) > + goto out; > + > + WRITE_ONCE(q->empty, false); > + if (likely(!test_bit(__QDISC_STATE_DEACTIVATED, > + &q->state))) > + quota = __qdisc_run(q); > + if (quota > 0) > + WRITE_ONCE(q->empty, true); > + qdisc_run_end(q); > } > > +out: > if (unlikely(to_free)) > kfree_skb_list(to_free); > return rc; > diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c > index 5ab696efca95..1bd2c4e9c4c2 100644 > --- a/net/sched/sch_generic.c > +++ b/net/sched/sch_generic.c > @@ -376,7 +376,7 @@ static inline bool qdisc_restart(struct Qdisc *q, int *packets) > return sch_direct_xmit(skb, q, dev, txq, root_lock, validate); > } > > -void __qdisc_run(struct Qdisc *q) > +int __qdisc_run(struct Qdisc *q) > { > int quota = dev_tx_weight; > int packets; > @@ -388,6 +388,7 @@ void __qdisc_run(struct Qdisc *q) > break; > } > } > + return quota; > } > > unsigned long dev_trans_start(struct net_device *dev) > @@ -649,12 +650,9 @@ static struct sk_buff *pfifo_fast_dequeue(struct Qdisc *qdisc) > > skb = __skb_array_consume(q); > } > - if (likely(skb)) { > - qdisc_update_stats_at_dequeue(qdisc, skb); > - } else { > - WRITE_ONCE(qdisc->empty, true); > - } > > + if (likely(skb)) > + qdisc_update_stats_at_dequeue(qdisc, skb); > return skb; > } > > > -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |