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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,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 99872C433DF for ; Thu, 15 Oct 2020 03:04:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 46DB522241 for ; Thu, 15 Oct 2020 03:04:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726323AbgJODEW (ORCPT ); Wed, 14 Oct 2020 23:04:22 -0400 Received: from mga11.intel.com ([192.55.52.93]:11510 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725919AbgJODEV (ORCPT ); Wed, 14 Oct 2020 23:04:21 -0400 IronPort-SDR: Y7c3yFEJJkGd5mTmPwDvnN3bx/YcJEO4xrvXuOVmWMAwDp49WDuVDMHUVp2WZQ51FlGpiKA26v LN3CvAGyJsiw== X-IronPort-AV: E=McAfee;i="6000,8403,9774"; a="162780266" X-IronPort-AV: E=Sophos;i="5.77,377,1596524400"; d="scan'208";a="162780266" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Oct 2020 20:04:20 -0700 IronPort-SDR: U4Kvq3YPtgyHV1+ezff4hfjksuKRU5TyuOHxHCCa6vqQc+6QbBwuM4RFrsKbhJ0imJH2k/IF9D sPZoNEYZu7Dw== X-IronPort-AV: E=Sophos;i="5.77,377,1596524400"; d="scan'208";a="314365473" Received: from shaunabu-mobl1.amr.corp.intel.com (HELO [10.254.101.5]) ([10.254.101.5]) by orsmga003-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Oct 2020 20:04:19 -0700 Subject: Re: [PATCH v6 2/2] PCI/ERR: Split the fatal and non-fatal error recovery handling To: Ethan Zhao Cc: Kuppuswamy Sathyanarayanan , Bjorn Helgaas , Sinan Kaya , linux-pci , Linux Kernel Mailing List , Ashok Raj References: <546d346644654915877365b19ea534378db0894d.1602663397.git.sathyanarayanan.kuppuswamy@linux.intel.com> <17e142b8-b19a-0ec7-833b-7a4ac2e76d0d@linux.intel.com> From: "Kuppuswamy, Sathyanarayanan" Message-ID: Date: Wed, 14 Oct 2020 20:04:17 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On 10/14/20 6:58 PM, Ethan Zhao wrote: > On Thu, Oct 15, 2020 at 1:06 AM Kuppuswamy, Sathyanarayanan > wrote: >> >> >> >> On 10/14/20 8:07 AM, Ethan Zhao wrote: >>> On Wed, Oct 14, 2020 at 5:00 PM Kuppuswamy Sathyanarayanan >>> wrote: >>>> >>>> Commit bdb5ac85777d ("PCI/ERR: Handle fatal error recovery") >>>> merged fatal and non-fatal error recovery paths, and also made >>>> recovery code depend on hotplug handler for "remove affected >>>> device + rescan" support. But this change also complicated the >>>> error recovery path and which in turn led to the following >>>> issues. >>>> >>>> 1. We depend on hotplug handler for removing the affected >>>> devices/drivers on DLLSC LINK down event (on DPC event >>>> trigger) and DPC handler for handling the error recovery. Since >>>> both handlers operate on same set of affected devices, it leads >>>> to race condition, which in turn leads to NULL pointer >>>> exceptions or error recovery failures.You can find more details >>>> about this issue in following link. >>>> >>>> https://lore.kernel.org/linux-pci/20201007113158.48933-1-haifeng.zhao@intel.com/T/#t >>>> >>>> 2. For non-hotplug capable devices fatal (DPC) error recovery >>>> is currently broken. Current fatal error recovery implementation >>>> relies on PCIe hotplug (pciehp) handler for detaching and >>>> re-enumerating the affected devices/drivers. So when dealing with >>>> non-hotplug capable devices, recovery code does not restore the state >>>> of the affected devices correctly. You can find more details about >>>> this issue in the following links. >>>> >>>> https://lore.kernel.org/linux-pci/20200527083130.4137-1-Zhiqiang.Hou@nxp.com/ >>>> https://lore.kernel.org/linux-pci/12115.1588207324@famine/ >>>> https://lore.kernel.org/linux-pci/0e6f89cd6b9e4a72293cc90fafe93487d7c2d295.1585000084.git.sathyanarayanan.kuppuswamy@linux.intel.com/ >>>> >>>> In order to fix the above two issues, we should stop relying on hotplug >>> Yes, it doesn't rely on hotplug handler to remove and rescan the device, >>> but it couldn't prevent hotplug drivers from doing another replicated >>> removal/rescanning. >>> it doesn't make sense to leave another useless removal/rescanning there. >>> Maybe that's why these two paths were merged to one and made it rely on >>> hotplug. >> No, as per PCIe spec, hotplug and DPC has no functional dependency. Hence >> depending on it to handle some of its recovery function is in-correct and >> would lead to issues in non-hotplug capable platforms (which is true >> currently). >>> > pci_lock_rescan_remove() is global lock for PCIe, the mal-functional > device's port holds this lock, it prevents the whole system from doing > hot-plug operation. It does not prevent the hotplug operation, but it might delay it. Since both DPC and hotplug operates on same set of devices, it must be synchronized. > Though pciehp is not so hot/scalable and performance critical, but there > is per cpu thread to handle hot-plug operation. synchronize all threads > make them walk backwards for scalability. DPC events does not happen in high frequency. So I don't think we should worry about the performance here. Even hotplug handler will hold this lock when adding/removing the devices. So adding/removing devices is a serialized operation. > >> >>>> -- >>>> 2.17.1 >>>> >> >> -- >> Sathyanarayanan Kuppuswamy >> Linux Kernel Developer -- Sathyanarayanan Kuppuswamy Linux Kernel Developer