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=-7.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 C0E70C433E0 for ; Wed, 13 May 2020 22:44:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B59952065C for ; Wed, 13 May 2020 22:44:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589409894; bh=SaXEtxehBPXNgHzxv6SxCYt0qjGeXgQurv3G6wTPpAU=; h=Date:From:To:Cc:Subject:In-Reply-To:List-ID:From; b=SQfqoFjpUFZSb+aQPCdpIVrK0GfNjyfTK2S3neBX2YN0B1fCS9lORKdoTMDmKyjrF FwAlVbgsmGWspiOh0WxmNp8JvMg0MfoJZw9LHLek/o9Pczy/wfWMOSyNaMcsQ3BPU0 BxOSgTzKLAGGcfzLn1VRj9wd3ZBITCYVukZ/1TBQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731644AbgEMWoy (ORCPT ); Wed, 13 May 2020 18:44:54 -0400 Received: from mail.kernel.org ([198.145.29.99]:59166 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731497AbgEMWox (ORCPT ); Wed, 13 May 2020 18:44:53 -0400 Received: from localhost (mobile-166-175-190-200.mycingular.net [166.175.190.200]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B6F6F204EF; Wed, 13 May 2020 22:44:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589409892; bh=SaXEtxehBPXNgHzxv6SxCYt0qjGeXgQurv3G6wTPpAU=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=jbkIbctTPcxjp+MFlS9oh6QvN2AiF2pz772yweD79fJfp5R4pmoh8sihgRDr31Lav IUfFd49RzCmsgnizlgF9BHMgD1CVdlWZ63DRybM2zpY2nqzKreSWGjcvaTuKDI61Gi +BsgJBAV2aV7sHg9VFkYnYGeM+cY7IfZIEKAqlao= Date: Wed, 13 May 2020 17:44:49 -0500 From: Bjorn Helgaas To: sathyanarayanan.kuppuswamy@linux.intel.com Cc: bhelgaas@google.com, jay.vosburgh@canonical.com, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, ashok.raj@intel.com Subject: Re: [PATCH v1 1/1] PCI/ERR: Handle fatal error recovery for non-hotplug capable devices Message-ID: <20200513224449.GA347443@bjorn-Precision-5520> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 06, 2020 at 08:32:59PM -0700, 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. Apparently this fixes a bug. Can you include a link to a problem report? The above is a description of a *solution*, but it's hard to understand without starting with the problem itself. The above talks about reset_link(), which is only used in the io_frozen case. In that case, I think the only thing this patch changes is that when reset_link() fails, we'll return with PCI_ERS_RESULT_DISCONNECT instead of whatever reset_link() returned. What this patch *does* change is that in the normal_detected case, we previously never called reset_link() but now we will if an .error_detected() callback requested it. > 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. Sorry, I'm not following this explanation. IIUC this fixes a bug when the channel is frozen and .error_detected() returns NEED_RESET. In that case, the current code does: * state == io_frozen * .error_detected() returns status == NEED_RESET * status = reset_link() * if status != RECOVERED, we return status * otherwise status == RECOVERED * we do not call report_slot_reset() * we return RECOVERED It does seem like we *should* call the .slot_reset() callbacks, but the only time we return recovery failure is if reset_link() failed. I can certainly understand if drivers don't recover when we reset their device but don't call their .slot_reset() callback. Is that what this fixes? After the patch, * state == io_frozen * .error_detected() returns status == NEED_RESET * we set status = NEED_RESET (doesn't change anything in this case) * we call reset_link() * if reset_link() failed, we return DISCONNECT * otherwise continue with status == NEED_RESET * we *do* call report_slot_reset() * we return whatever .slot_reset() returned I think the change to call .slot_reset() makes sense, but that's not at all clear from the commit log. Am I understanding the behavior correctly? > 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. Use "pcie_do_recovery()" and "report_slot_reset()" (including the parentheses) to follow convention. Also fix other occurrences above. > [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) > + status = PCI_ERS_RESULT_DISCONNECT; > + } else { > + if (pci_bus_error_reset(dev)) > + status = PCI_ERS_RESULT_DISCONNECT; As far as I can tell, there is no caller of pcie_do_recovery() where reset_link is NULL, so this call of pci_bus_error_reset() looks like dead code. We did not previously check whether reset_link was NULL, and this patch changes nothing that could result in it being NULL. > + } > + > + 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) { > -- > 2.17.1 >