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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 3D6D3C4360C for ; Tue, 8 Oct 2019 22:06:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1C6C721924 for ; Tue, 8 Oct 2019 22:06:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725879AbfJHWGs (ORCPT ); Tue, 8 Oct 2019 18:06:48 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52902 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725848AbfJHWGs (ORCPT ); Tue, 8 Oct 2019 18:06:48 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id CDCE110CC1E9; Tue, 8 Oct 2019 22:06:47 +0000 (UTC) Received: from [10.3.117.216] (ovpn-117-216.phx2.redhat.com [10.3.117.216]) by smtp.corp.redhat.com (Postfix) with ESMTP id CE8535D71C; Tue, 8 Oct 2019 22:06:46 +0000 (UTC) Subject: Re: [PATCH] PCI/IOV: update num_VFs earlier To: Bjorn Helgaas , CREGUT Pierre IMT/OLN Cc: linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, Alexander Duyck , Jakub Kicinski References: <20191008213835.GA230403@google.com> From: Don Dutile Message-ID: <4ac38c7a-b8d4-9a1c-10ab-ce8b4cf2991f@redhat.com> Date: Tue, 8 Oct 2019 18:06:46 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20191008213835.GA230403@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.65]); Tue, 08 Oct 2019 22:06:48 +0000 (UTC) Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On 10/08/2019 05:38 PM, Bjorn Helgaas wrote: > On Thu, Oct 03, 2019 at 05:10:07PM -0500, Bjorn Helgaas wrote: >> On Thu, Oct 03, 2019 at 11:04:45AM +0200, CREGUT Pierre IMT/OLN wrote: >>> ... > >>> NIC drivers send netlink events when their state change, but it is >>> the core that changes the value of num_vfs. So I would think it is >>> the core responsibility to make sure the exposed value makes sense >>> and it would be better to ignore the details of the driver >>> implementation. >> >> Yes, I think you're right. And I like your previous suggestion of >> just locking the device in the reader. I'm not enough of a sysfs >> expert to know if there's a good reason to avoid a lock there. Does >> the following look reasonable to you? > > I applied the patch below to pci/virtualization for v5.5, thanks for I hope not... see below > your great patience! > >> commit 0940fc95da45 >> Author: Pierre Crégut >> Date: Wed Sep 11 09:27:36 2019 +0200 >> >> PCI/IOV: Serialize sysfs sriov_numvfs reads vs writes >> >> When sriov_numvfs is being updated, drivers may notify about new devices >> before they are reflected in sriov->num_VFs, so concurrent sysfs reads >> previously returned stale values. >> >> Serialize the sysfs read vs the write so the read returns the correct >> num_VFs value. >> >> Link: https://bugzilla.kernel.org/show_bug.cgi?id=202991 >> Link: https://lore.kernel.org/r/20190911072736.32091-1-pierre.cregut@orange.com >> Signed-off-by: Pierre Crégut >> Signed-off-by: Bjorn Helgaas >> >> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c >> index b3f972e8cfed..e77562aabbae 100644 >> --- a/drivers/pci/iov.c >> +++ b/drivers/pci/iov.c >> @@ -254,8 +254,14 @@ static ssize_t sriov_numvfs_show(struct device *dev, >> char *buf) >> { >> struct pci_dev *pdev = to_pci_dev(dev); >> + u16 num_vfs; >> + >> + /* Serialize vs sriov_numvfs_store() so readers see valid num_VFs */ >> + device_lock(&pdev->dev); ^^^^^ lock >> + num_vfs = pdev->sriov->num_VFs; >> + device_lock(&pdev->dev); ^^^^ and lock again! >> >> - return sprintf(buf, "%u\n", pdev->sriov->num_VFs); >> + return sprintf(buf, "%u\n", num_vfs); >> } >> >> /*