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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 C9A23C433DF for ; Wed, 27 May 2020 03:49:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9C3942084C for ; Wed, 27 May 2020 03:49:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726408AbgE0Dtn (ORCPT ); Tue, 26 May 2020 23:49:43 -0400 Received: from szxga06-in.huawei.com ([45.249.212.32]:46204 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726277AbgE0Dtn (ORCPT ); Tue, 26 May 2020 23:49:43 -0400 Received: from DGGEMS403-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id 49D9AD86C77125540178; Wed, 27 May 2020 11:49:41 +0800 (CST) Received: from [10.65.58.147] (10.65.58.147) by DGGEMS403-HUB.china.huawei.com (10.3.19.203) with Microsoft SMTP Server id 14.3.487.0; Wed, 27 May 2020 11:49:36 +0800 Subject: Re: [PATCH v1 1/1] PCI/ERR: Handle fatal error recovery for non-hotplug capable devices To: "Kuppuswamy, Sathyanarayanan" , References: <18609.1588812972@famine> <2569c75c-41a6-d0f3-ee34-0d288c4e0b61@linux.intel.com> <8dd2233c-a636-59fa-4c6e-5da08556d09e@hisilicon.com> CC: , , , From: Yicong Yang Message-ID: Date: Wed, 27 May 2020 11:50:01 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.65.58.147] X-CFilter-Loop: Reflected Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org Hi, On 2020/5/27 9:31, Kuppuswamy, Sathyanarayanan wrote: > Hi, > > On 5/21/20 7:56 PM, Yicong Yang wrote: >> >> >> On 2020/5/22 3:31, Kuppuswamy, Sathyanarayanan wrote: >>> >>> >>> On 5/21/20 3:58 AM, Yicong Yang wrote: >>>> On 2020/5/21 1:04, Kuppuswamy, Sathyanarayanan wrote: >>>>> >>>>> >>>>> On 5/20/20 1:28 AM, Yicong Yang wrote: >>>>>> On 2020/5/7 11:32, sathyanarayanan.kuppuswamy@linux.intel.com wrote: >>>>>>> From: Kuppuswamy Sathyanarayanan >>>>>>> >>>>>>> If there are non-hotplug capable devices connected to a given >>>>>>> port, then during the fatal error recovery(triggered by DPC or >>>>>>> AER), after calling reset_link() function, we cannot rely on >>>>>>> hotplug handler to detach and re-enumerate the device drivers >>>>>>> in the affected bus. Instead, we will have to let the error >>>>>>> recovery handler call report_slot_reset() for all devices in >>>>>>> the bus to notify about the reset operation. Although this is >>>>>>> only required for non hot-plug capable devices, doing it for >>>>>>> hotplug capable devices should not affect the functionality. >>>>>>> >>>>>>> Along with above issue, this fix also applicable to following >>>>>>> issue. >>>>>>> >>>>>>> Commit 6d2c89441571 ("PCI/ERR: Update error status after >>>>>>> reset_link()") added support to store status of reset_link() >>>>>>> call. Although this fixed the error recovery issue observed if >>>>>>> the initial value of error status is PCI_ERS_RESULT_DISCONNECT >>>>>>> or PCI_ERS_RESULT_NO_AER_DRIVER, it also discarded the status >>>>>>> result from report_frozen_detected. This can cause a failure to >>>>>>> recover if _NEED_RESET is returned by report_frozen_detected and >>>>>>> report_slot_reset is not invoked. >>>>>>> >>>>>>> Such an event can be induced for testing purposes by reducing the >>>>>>> Max_Payload_Size of a PCIe bridge to less than that of a device >>>>>>> downstream from the bridge, and then initiating I/O through the >>>>>>> device, resulting in oversize transactions. In the presence of DPC, >>>>>>> this results in a containment event and attempted reset and recovery >>>>>>> via pcie_do_recovery. After 6d2c89441571 report_slot_reset is not >>>>>>> invoked, and the device does not recover. >>>>>>> >>>>>>> [original patch is from jay.vosburgh@canonical.com] >>>>>>> [original patch link https://lore.kernel.org/linux-pci/18609.1588812972@famine/] >>>>>>> Fixes: 6d2c89441571 ("PCI/ERR: Update error status after reset_link()") >>>>>>> Signed-off-by: Jay Vosburgh >>>>>>> Signed-off-by: Kuppuswamy Sathyanarayanan >>>>>>> --- >>>>>>> drivers/pci/pcie/err.c | 19 +++++++++++++++---- >>>>>>> 1 file changed, 15 insertions(+), 4 deletions(-) >>>>>>> >>>>>>> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c >>>>>>> index 14bb8f54723e..db80e1ecb2dc 100644 >>>>>>> --- a/drivers/pci/pcie/err.c >>>>>>> +++ b/drivers/pci/pcie/err.c >>>>>>> @@ -165,13 +165,24 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev, >>>>>>> pci_dbg(dev, "broadcast error_detected message\n"); >>>>>>> if (state == pci_channel_io_frozen) { >>>>>>> pci_walk_bus(bus, report_frozen_detected, &status); >>>>>>> - status = reset_link(dev); >>>>>>> - if (status != PCI_ERS_RESULT_RECOVERED) { >>>>>>> + status = PCI_ERS_RESULT_NEED_RESET; >>>>>>> + } else { >>>>>>> + pci_walk_bus(bus, report_normal_detected, &status); >>>>>>> + } >>>>>>> + >>>>>>> + if (status == PCI_ERS_RESULT_NEED_RESET) { >>>>>>> + if (reset_link) { >>>>>>> + if (reset_link(dev) != PCI_ERS_RESULT_RECOVERED) >>>>>> >>>>>> we'll call reset_link() only if link is frozen. so it may have problem here. >>>>> you mean before this change right? >>>>> After this change, reset_link() will be called as long as status is >>>>> PCI_ERS_RESULT_NEED_RESET. >>>> >>>> Yes. I think we should reset the link only if the io is blocked as before. There's >>>> no reason to reset a normal link. >>> Currently, only AER and DPC driver uses pcie_do_recovery() call. So the >>> possible reset_link options are dpc_reset_link() and aer_root_reset(). >>> >>> In dpc_reset_link() case, the link is already disabled and hence we >>> don't need to do another reset. In case of aer_root_reset() it >>> uses pci_bus_error_reset() to reset the slot. >> >> Not exactly. In pci_bus_error_reset(), we call pci_slot_reset() only if it's >> hotpluggable. But we always call pci_bus_reset() to perform a secondary bus >> reset for the bridge. That's what I think is unnecessary for a normal link, >> and that's what reset link indicates us to do. The slot reset is introduced >> in the process only to solve side effects. (c4eed62a2143, PCI/ERR: Use slot reset if available) > > IIUC, pci_bus_reset() will do slot reset if its supported (hot-plug > capable slots). If its not supported then it will attempt secondary > bus reset. So secondary bus reset will be attempted only if slot > reset is not supported. > > Since reported_error_detected() requests us to do reset, we will have > to attempt some kind of reset before we call ->slot_reset() right? > What is the side effect in calling secondary bus reset? I agree we should do a slot reset if driver required. The question is if we apply the patch, think of a situation that the io is normal, the slot is not hotpluggable but driver reports a reset, then: -->aer_root_reset() ----->pci_bus_error_reset() ---------> pci_bridge_secondary_bus_reset() // Is it necessary to reset if the link is not blocked? Before commit (c4eed62a2143, PCI/ERR: Use slot reset if available), the reset_link() for aer is -->aer_root_reset() ----->pci_bridge_secondary_bus_reset() As mentioned by the commit c4eed62a2143 "The secondary bus reset may have link side effects that a hotplug capable port may incorrectly react to. Use the slot specific reset for hotplug ports, fixing the undesirable link down-up handling during error recovering." So I assume it use hotplug slot reset rather than secondary bus reset to recover the link. If the link is normal, it's unnecessary to do so. so we should add a check before reset the link in the patch: + if (status == PCI_ERS_RESULT_NEED_RESET && + state == pci_channel_io_frozen) { We should do slot reset if driver required, but it's different from the `slot reset` in pci_bus_error_reset(). Previously we don't do a slot reset and call ->slot_reset() directly, I don't know the certain reason. Thanks, Yicong > >> >> PCI_ERS_RESULT_NEED_RESET indicates that the driver >> wants a platform-dependent slot reset and its ->slot_reset() method to be called then. >> I don't think it's same as slot reset mentioned above, which is only for hotpluggable >> ones. > What you think is the correct reset implementation ? Is it something > like this? > > if (hotplug capable) > try_slot_reset() > else > do_nothing() >> >> Previously, if link is normal and the driver reports PCI_ERS_RESULT_NEED_RESET, >> we'll only call ->slot_reset() without slot reset in reset_link(). Maybe it's better >> to perform just like before. >> >> Thanks. >> >> >>>> >>>> Furthermore, PCI_ERS_RESULT_NEED_RESET means device driver requires a slot reset rather >>>> than a link reset, so it maybe improper to use it to judge whether a link reset is needed. >>>> We decide whether to do a link reset only by the io state. >>>> >>>> Thanks, >>>> Yicong >>>> >>>> >>>>>> >>>>>> Thanks, >>>>>> Yicong >>>>>> >>>>>> >>>>>>> + status = PCI_ERS_RESULT_DISCONNECT; >>>>>>> + } else { >>>>>>> + if (pci_bus_error_reset(dev)) >>>>>>> + status = PCI_ERS_RESULT_DISCONNECT; >>>>>>> + } >>>>>>> + >>>>>>> + if (status == PCI_ERS_RESULT_DISCONNECT) { >>>>>>> pci_warn(dev, "link reset failed\n"); >>>>>>> goto failed; >>>>>>> } >>>>>>> - } else { >>>>>>> - pci_walk_bus(bus, report_normal_detected, &status); >>>>>>> } >>>>>>> if (status == PCI_ERS_RESULT_CAN_RECOVER) { >>>>>> >>>>> . >>>>> >>>> >>> . >>> >> > . >