From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754394AbdFNE5Z (ORCPT ); Wed, 14 Jun 2017 00:57:25 -0400 Received: from mx4.wp.pl ([212.77.101.11]:22769 "EHLO mx4.wp.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754379AbdFNE5W (ORCPT ); Wed, 14 Jun 2017 00:57:22 -0400 Date: Tue, 13 Jun 2017 21:57:13 -0700 From: Jakub Kicinski To: Bjorn Helgaas Cc: Bjorn Helgaas , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, Greg Kroah-Hartman , Emil Tantilov , Alexander Duyck , oss-drivers@netronome.com Subject: Re: [PATCH] pci: iov: use device lock to protect IOV sysfs accesses Message-ID: <20170613215713.42af408e@cakuba.netronome.com> In-Reply-To: <20170530163429.07977942@cakuba.lan> References: <20170522225023.14010-1-jakub.kicinski@netronome.com> <20170526234726.GD21531@bhelgaas-glaptop.roam.corp.google.com> <20170526165820.7ec488e3@cakuba.netronome.com> <20170530230718.GG14896@bhelgaas-glaptop.roam.corp.google.com> <20170530163429.07977942@cakuba.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-WP-MailID: da392900a7c4134ebffa68639828d4fb X-WP-AV: skaner antywirusowy Poczty Wirtualnej Polski X-WP-SPAM: NO 000000A [YcPk] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 30 May 2017 16:34:29 -0700, Jakub Kicinski wrote: > On Tue, 30 May 2017 18:07:18 -0500, Bjorn Helgaas wrote: > > On Fri, May 26, 2017 at 04:58:20PM -0700, Jakub Kicinski wrote: > > > On Fri, 26 May 2017 18:47:26 -0500, Bjorn Helgaas wrote: > > > > On Mon, May 22, 2017 at 03:50:23PM -0700, Jakub Kicinski wrote: > > > > > PCI core sets the driver pointer before calling ->probe() and only > > > > > clears it after ->remove(). This means driver's ->sriov_configure() > > > > > callback will happily race with probe() and remove(), most likely > > > > > leading to BUGs, since drivers don't expect this. > > > > > > > > I guess you're referring to the pci_dev->driver pointer set by > > > > local_pci_probe(), and this is important because sriov_numvfs_store() > > > > checks that pointer, right? > > > > > > Yes, exactly. I initially thought this is how the safety of sriov > > > callback may have been ensured, but since the order of > > > local_pci_probe() and the assignment is what it is, it can't. > > > > Right. I was hoping other subsystems would establish a convention > > about whether we set the ->driver pointer before or after calling the > > driver probe() method, but if there is one, I don't see it. > > local_pci_probe() and really_probe() set ->driver first, but > > pnp_device_probe() calls the probe() method first. > > I didn't dig into reordering the pointer setting, to be honest. I > thought establishing that driver callbacks should generally hold device > lock, whenever possible, would be even better than pointer setting > conventions. > > If we order the assignments better, wouldn't we still need appropriate > memory barriers to rely on the order? (: > > > Can you expand on how you reproduce this problem? The only real way I > > see to call ->sriov_configure() is via the sysfs entry point, and I > > would think user-space code would typically not touch that until after > > it knows the driver has claimed a device. But I can certainly imagine > > targeted test code that could hit this problem. > > Correct. It's not something that users should be triggering often in > normal use. I also found it by code inspection rather than by getting > an oops. > > OTOH if the driver performs FW load or other time-consuming operations > in ->probe() the time window when this can be triggered may be counted > in seconds. Hi Bjorn, is this patch still considered for 4.13, or should I change it somehow?