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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 C2382C282DD for ; Wed, 8 Jan 2020 14:55:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 88D57206F0 for ; Wed, 8 Jan 2020 14:55:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728730AbgAHOzg (ORCPT ); Wed, 8 Jan 2020 09:55:36 -0500 Received: from metis.ext.pengutronix.de ([85.220.165.71]:54361 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726556AbgAHOzg (ORCPT ); Wed, 8 Jan 2020 09:55:36 -0500 Received: from gallifrey.ext.pengutronix.de ([2001:67c:670:201:5054:ff:fe8d:eefb] helo=[127.0.0.1]) by metis.ext.pengutronix.de with esmtp (Exim 4.92) (envelope-from ) id 1ipCkB-0003ef-Bn; Wed, 08 Jan 2020 15:55:35 +0100 To: linux-can@vger.kernel.org, netdev@vger.kernel.org, pabeni@redhat.com From: Ahmad Fatoum Subject: [BUG] pfifo_fast may cause out-of-order CAN frame transmission Cc: Sascha Hauer Message-ID: <661cc33a-5f65-2769-cc1a-65791cb4b131@pengutronix.de> Date: Wed, 8 Jan 2020 15:55:34 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 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, 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: ba27b4cdaaa ("net: dev: introduce support for sch BYPASS for lockless qdisc") With it, using pfifo_fast, every few hundred frames, FlexCAN's .ndo_start_xmit is passed frames in an order different from how userspace stuffed them into the same socket. Reverting it fixes the issue as does booting with maxcpus=1 or using pfifo instead of pfifo_fast. According to [1], such reordering shouldn't be happening. Details on my setup: Kernel version: v5.5-rc5, (occurs much more often with LOCKDEP turned on) CAN-Bitrate: 250 kbit/s CAN frames are generated with: cangen canX -I2 -L1 -Di -i -g0.12 -p 100 which keeps polling after ENOBUFS until socket is writable, sends out a CAN frame with one incrementing payload byte and then waits 120 usec before repeating. Please let me know if any additional info is needed. Cheers Ahmad [1]: http://linux-tc-notes.sourceforge.net/tc/doc/sch_pfifo_fast.txt -- 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 |