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=-17.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 64FD3C43333 for ; Fri, 5 Feb 2021 23:23:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2C60C64FCA for ; Fri, 5 Feb 2021 23:23:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230258AbhBEXWj (ORCPT ); Fri, 5 Feb 2021 18:22:39 -0500 Received: from mail.kernel.org ([198.145.29.99]:52656 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230139AbhBEKFm (ORCPT ); Fri, 5 Feb 2021 05:05:42 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id DC7E464FD8; Fri, 5 Feb 2021 10:04:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1612519493; bh=28PKurE22BswmWny+JOPpHCzycquk/wHe2fKb6YjBhI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=GRMFjIMg0WDAfhXcZ/ESL0lo8tviyCl2qwH4O0+oHY8sHJdh09d/d8r86TI2w2Btj AckC5f6l4QHWok0G1jdmoszO97+cmgVN713MWIYMgw2vkuaIDaHWCGvttlEO1nBM1d iFfdBDb3IPsH7pdwJwNpm9a+7KmPQBsMJGsPATpNyWZIKOrs2jkNj/kAd9HLwi8qEM 9GpaACn2oT7I09+zOx27KRcy+SIThThBuonPZ6vcqCWA2FuWX12vrN9XhWD0NSmfWs hHOUgvJQ00vjc0iZQUilD8KK+iphwnHHtlPVahgvJYwvFmE4BOkz8ylSK6T3OLuXdF gmxHQk1GPOiiA== Received: by pali.im (Postfix) id 3CEE18A2; Fri, 5 Feb 2021 11:04:50 +0100 (CET) Date: Fri, 5 Feb 2021 11:04:49 +0100 From: Pali =?utf-8?B?Um9ow6Fy?= To: Daniel Vetter Cc: Bjorn Helgaas , LKML , Stephen Rothwell , linux-samsung-soc , Jan Kara , Kees Cook , Greg Kroah-Hartman , Linux PCI , Linux MM , Jason Gunthorpe , =?utf-8?B?SsOpcsO0bWU=?= Glisse , John Hubbard , Bjorn Helgaas , Daniel Vetter , Dan Williams , Andrew Morton , Linux ARM , "open list:DMA BUFFER SHARING FRAMEWORK" , Oliver O'Halloran , Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= Subject: Re: [PATCH 1/2] PCI: also set up legacy files only after sysfs init Message-ID: <20210205100449.w2vzqozgnolxqh4h@pali> References: <20210204165831.2703772-2-daniel.vetter@ffwll.ch> <20210204215019.GA104698@bjorn-Precision-5520> <20210204222407.pkx7wvmcvugdwqdd@pali> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: NeoMutt/20180716 Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Friday 05 February 2021 10:59:50 Daniel Vetter wrote: > On Thu, Feb 4, 2021 at 11:24 PM Pali Rohár wrote: > > > > On Thursday 04 February 2021 15:50:19 Bjorn Helgaas wrote: > > > [+cc Oliver, Pali, Krzysztof] > > > > Just to note that extending or using sysfs_initialized introduces > > another race condition into kernel code which results in PCI fatal > > errors. Details are in email discussion which Bjorn already sent. > > Yeah I wondered why this doesn't race. It races, but with smaller probability. I have not seen this race condition on x86. But I was able to reproduce it with native PCIe drivers on ARM64 (Marvell Armada 3720; pci-aardvark). In mentioned discussion I wrote when this race condition happen. But I understand that it is hard to simulate it. > but since the history goes back > to pre-git times I figured it would have been addressed somehow > already if it indeed does race. > -Daniel > > > > s/also/Also/ in subject > > > > > > On Thu, Feb 04, 2021 at 05:58:30PM +0100, Daniel Vetter wrote: > > > > We are already doing this for all the regular sysfs files on PCI > > > > devices, but not yet on the legacy io files on the PCI buses. Thus far > > > > now problem, but in the next patch I want to wire up iomem revoke > > > > support. That needs the vfs up an running already to make so that > > > > iomem_get_mapping() works. > > > > > > s/now problem/no problem/ > > > s/an running/and running/ > > > s/so that/sure that/ ? > > > > > > iomem_get_mapping() doesn't exist; I don't know what that should be. > > > > > > > Wire it up exactly like the existing code. Note that > > > > pci_remove_legacy_files() doesn't need a check since the one for > > > > pci_bus->legacy_io is sufficient. > > > > > > I'm not sure exactly what you mean by "the existing code." I could > > > probably figure it out, but it would save time to mention the existing > > > function here. > > > > > > This looks like another instance where we should really apply Oliver's > > > idea of converting these to attribute_groups [1]. > > > > > > The cover letter mentions options discussed with Greg in [2], but I > > > don't think the "sysfs_initialized" hack vs attribute_groups was part > > > of that discussion. > > > > > > It's not absolutely a show-stopper, but it *is* a shame to extend the > > > sysfs_initialized hack if attribute_groups could do this more cleanly > > > and help solve more than one issue. > > > > > > Bjorn > > > > > > [1] https://lore.kernel.org/r/CAOSf1CHss03DBSDO4PmTtMp0tCEu5kScn704ZEwLKGXQzBfqaA@mail.gmail.com > > > [2] https://lore.kernel.org/dri-devel/CAKMK7uGrdDrbtj0OyzqQc0CGrQwc2F3tFJU9vLfm2jjufAZ5YQ@mail.gmail.com/ > > > > > > > Signed-off-by: Daniel Vetter > > > > Cc: Stephen Rothwell > > > > Cc: Jason Gunthorpe > > > > Cc: Kees Cook > > > > Cc: Dan Williams > > > > Cc: Andrew Morton > > > > Cc: John Hubbard > > > > Cc: Jérôme Glisse > > > > Cc: Jan Kara > > > > Cc: Dan Williams > > > > Cc: Greg Kroah-Hartman > > > > Cc: linux-mm@kvack.org > > > > Cc: linux-arm-kernel@lists.infradead.org > > > > Cc: linux-samsung-soc@vger.kernel.org > > > > Cc: linux-media@vger.kernel.org > > > > Cc: Bjorn Helgaas > > > > Cc: linux-pci@vger.kernel.org > > > > --- > > > > drivers/pci/pci-sysfs.c | 7 +++++++ > > > > 1 file changed, 7 insertions(+) > > > > > > > > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c > > > > index fb072f4b3176..0c45b4f7b214 100644 > > > > --- a/drivers/pci/pci-sysfs.c > > > > +++ b/drivers/pci/pci-sysfs.c > > > > @@ -927,6 +927,9 @@ void pci_create_legacy_files(struct pci_bus *b) > > > > { > > > > int error; > > > > > > > > + if (!sysfs_initialized) > > > > + return; > > > > + > > > > b->legacy_io = kcalloc(2, sizeof(struct bin_attribute), > > > > GFP_ATOMIC); > > > > if (!b->legacy_io) > > > > @@ -1448,6 +1451,7 @@ void pci_remove_sysfs_dev_files(struct pci_dev *pdev) > > > > static int __init pci_sysfs_init(void) > > > > { > > > > struct pci_dev *pdev = NULL; > > > > + struct pci_bus *pbus = NULL; > > > > int retval; > > > > > > > > sysfs_initialized = 1; > > > > @@ -1459,6 +1463,9 @@ static int __init pci_sysfs_init(void) > > > > } > > > > } > > > > > > > > + while ((pbus = pci_find_next_bus(pbus))) > > > > + pci_create_legacy_files(pbus); > > > > + > > > > return 0; > > > > } > > > > late_initcall(pci_sysfs_init); > > > > -- > > > > 2.30.0 > > > > > > > > > > > > _______________________________________________ > > > > linux-arm-kernel mailing list > > > > linux-arm-kernel@lists.infradead.org > > > > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > > > > -- > Daniel Vetter > Software Engineer, Intel Corporation > http://blog.ffwll.ch