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=-4.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 B3B20C433DF for ; Thu, 8 Oct 2020 19:59:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4377222227 for ; Thu, 8 Oct 2020 19:59:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602187151; bh=KWdIgJ4CVgfBZIUsekfpN9Om9ak7TjpRtxfSQOUshhs=; h=Date:From:To:Cc:Subject:In-Reply-To:List-ID:From; b=DVSTMmUGdy3EW/FK4rp0t4pdiaLNRGg+7kYOcLGIRuSRekAmWnccmwctiCdEKPPgl t7rb5AUmPMFFNqFimy57hTa0t6ERaEm/xylief4VBAuAN2OfVfV1Z5mPZNk7We92n4 5hZaGg1B/3Y6+f38e/dfOlJJIAN9Ww7CsG0SFOUM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729397AbgJHT7K (ORCPT ); Thu, 8 Oct 2020 15:59:10 -0400 Received: from mail.kernel.org ([198.145.29.99]:36738 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728202AbgJHT7K (ORCPT ); Thu, 8 Oct 2020 15:59:10 -0400 Received: from localhost (170.sub-72-107-125.myvzw.com [72.107.125.170]) (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 591F822226; Thu, 8 Oct 2020 19:59:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602187149; bh=KWdIgJ4CVgfBZIUsekfpN9Om9ak7TjpRtxfSQOUshhs=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=yeDUnG4Hm2+POoWDHW6sZ+B2vjjBat3MDJRzdmhfVOHzqGI1AYTMYmIJwU5pUD02v Yexa4A2DUPZSSqSUhHndLXs3/BAGxb1DJm6gIRsDTsPH/weOSFLukxnZgUf0Lv2ydt L8kt0htX3o6qDBG7gv19Pnzi4eAho+hgRV1Xz+cE= Date: Thu, 8 Oct 2020 14:59:07 -0500 From: Bjorn Helgaas To: Pali =?iso-8859-1?Q?Roh=E1r?= Cc: Oliver O'Halloran , Bjorn Helgaas , linux-pci , Linux Kernel Mailing List , Lorenzo Pieralisi , Gregory Clement , Andrew Lunn , Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= , Yinghai Lu Subject: Re: PCI: Race condition in pci_create_sysfs_dev_files Message-ID: <20201008195907.GA3359851@bjorn-Precision-5520> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20201007161434.GA3247067@bjorn-Precision-5520> Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Wed, Oct 07, 2020 at 11:14:34AM -0500, Bjorn Helgaas wrote: > On Wed, Oct 07, 2020 at 10:14:00AM +0200, Pali Rohár wrote: > > On Wednesday 07 October 2020 12:47:40 Oliver O'Halloran wrote: > > > On Wed, Oct 7, 2020 at 10:26 AM Bjorn Helgaas wrote: > > > > > > > > I'm not really a fan of this because pci_sysfs_init() is a bit of a > > > > hack to begin with, and this makes it even more complicated. > > > > > > > > It's not obvious from the code why we need pci_sysfs_init(), but > > > > Yinghai hinted [1] that we need to create sysfs after assigning > > > > resources. I experimented by removing pci_sysfs_init() and skipping > > > > the ROM BAR sizing. In that case, we create sysfs files in > > > > pci_bus_add_device() and later assign space for the ROM BAR, so we > > > > fail to create the "rom" sysfs file. > > > > > > > > The current solution to that is to delay the sysfs files until > > > > pci_sysfs_init(), a late_initcall(), which runs after resource > > > > assignments. But I think it would be better if we could create the > > > > sysfs file when we assign the BAR. Then we could get rid of the > > > > late_initcall() and that implicit ordering requirement. > > > > > > You could probably fix that by using an attribute_group to control > > > whether the attribute shows up in sysfs or not. The .is_visible() for > > > the group can look at the current state of the device and hide the rom > > > attribute if the BAR isn't assigned or doesn't exist. That way we > > > don't need to care when the actual assignment occurs. > > > > And cannot we just return e.g. -ENODATA (or other error code) for those > > problematic sysfs nodes until late_initcall() is called? > > I really like Oliver's idea and I think we should push on that to see > if it can be made to work. If so, we can remove the late_initcall() > completely. > > > > > But I haven't tried to code it up, so it's probably more complicated > > > > than this. I guess ideally we would assign all the resources before > > > > pci_bus_add_device(). If we could do that, we could just remove > > > > pci_sysfs_init() and everything would just work, but I think that's a > > > > HUGE can of worms. > > > > > > I was under the impression the whole point of pci_bus_add_device() was > > > to handle any initialisation that needed to be done after resources > > > were assigned. Is the ROM BAR being potentially unassigned an x86ism > > > or is there some bigger point I'm missing? > > We can't assign resources for each device as we enumerate it because > we don't know what's in use by other devices yet to be enumerated. > That part is generic, not x86-specific. > > The part that is x86-specific (or at least specific to systems using > ACPI) is that the ACPI core doesn't reserve resources used by ACPI > devices. Sometimes those resources are included in the PCI host > bridge windows, and we don't want to assign them to PCI devices. > > I didn't trace this all the way, but the pcibios_assign_resources() > and pnp_system_init() comments look relevant. It's a little concerning > that they're both fs_initcalls() and the ordering looks important, but > it would only be by accident of link ordering that pnp_system_init() > happens first. Pali, what's your thought on this? Do you plan to work on this yourself? If not and if you can live with your workaround a while longer, I think Krzysztof might be interested in taking a crack at it. I would just hate to see you guys duplicate each others' work :) Bjorn