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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FAKE_REPLY_C,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,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 7BCB5C10F14 for ; Tue, 8 Oct 2019 21:38:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3B49021835 for ; Tue, 8 Oct 2019 21:38:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570570721; bh=11TBIQmvDjjaIrom74PlC3QwYOcWo8Yzh1UnY6FDcXM=; h=Date:From:To:Cc:Subject:In-Reply-To:List-ID:From; b=2ejjIcDO1mnBkoIQW0JIvK/5MkI3k056ewVn8HiqKlipd/gfmxC8K6sTdYT60JjXB 9T87QSXRpvx5F5n8Wao3aL//7w0IMetUOtPPbMjLz2D+wVHFwrYcf5xef9a1oAt6fH iFXhRYLfQiCSZeKgP0CgAHacbZsNYLCU2BDyhm30= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729794AbfJHVik (ORCPT ); Tue, 8 Oct 2019 17:38:40 -0400 Received: from mail.kernel.org ([198.145.29.99]:58156 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727570AbfJHVik (ORCPT ); Tue, 8 Oct 2019 17:38:40 -0400 Received: from localhost (unknown [69.71.4.100]) (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 A2BB32070B; Tue, 8 Oct 2019 21:38:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570570719; bh=11TBIQmvDjjaIrom74PlC3QwYOcWo8Yzh1UnY6FDcXM=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=vdS3XsDJMxwTYD7JXt7NUIntQHVBVRlNiQi5xBv/fgLTIFcGeDhw+C0HfNW4Wjwh7 e+5qQwwp5LH8xUShakUgnUp7sCPg45gIVCt6ehJz+iXM6t+iqJVkhY+7zczyZ6lYul hBlMiNvw4LndkopNyp9a7E1JajpgAU8UTqbUqXNQ= Date: Tue, 8 Oct 2019 16:38:35 -0500 From: Bjorn Helgaas To: CREGUT Pierre IMT/OLN Cc: linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, Donald Dutile , Alexander Duyck , Jakub Kicinski Subject: Re: [PATCH] PCI/IOV: update num_VFs earlier Message-ID: <20191008213835.GA230403@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20191003221007.GA209602@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org 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 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); > + num_vfs = pdev->sriov->num_VFs; > + device_lock(&pdev->dev); > > - return sprintf(buf, "%u\n", pdev->sriov->num_VFs); > + return sprintf(buf, "%u\n", num_vfs); > } > > /*