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=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT 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 28208C4321D for ; Mon, 20 Aug 2018 07:17:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E03BA208FA for ; Mon, 20 Aug 2018 07:17:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E03BA208FA Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=wunner.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726661AbeHTKbe (ORCPT ); Mon, 20 Aug 2018 06:31:34 -0400 Received: from bmailout3.hostsharing.net ([176.9.242.62]:39095 "EHLO bmailout3.hostsharing.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726030AbeHTKbe (ORCPT ); Mon, 20 Aug 2018 06:31:34 -0400 Received: from h08.hostsharing.net (h08.hostsharing.net [83.223.95.28]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "*.hostsharing.net", Issuer "COMODO RSA Domain Validation Secure Server CA" (not verified)) by bmailout3.hostsharing.net (Postfix) with ESMTPS id 871AE1030CD10; Mon, 20 Aug 2018 09:17:03 +0200 (CEST) Received: by h08.hostsharing.net (Postfix, from userid 100393) id 3B5F57878D; Mon, 20 Aug 2018 09:17:03 +0200 (CEST) Date: Mon, 20 Aug 2018 09:17:03 +0200 From: Lukas Wunner To: Benjamin Herrenschmidt Cc: Bjorn Helgaas , linux-pci@vger.kernel.org, Hari Vyas , Ray Jui , Srinath Mannam , Guenter Roeck , Jens Axboe , Konstantin Khlebnikov , Marta Rybczynska , Pierre-Yves Kerbrat , linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 1/6] Revert "PCI: Fix is_added/is_busmaster race condition" Message-ID: <20180820071703.hnsyhb5pz4svb7jg@wunner.de> References: <20180817044902.31420-1-benh@kernel.crashing.org> <20180817044902.31420-2-benh@kernel.crashing.org> <20180817154431.GC128050@bhelgaas-glaptop.roam.corp.google.com> <06c1233b71dea08b1fc32334acefc48c32c46557.camel@kernel.crashing.org> <20180819022440.GG128050@bhelgaas-glaptop.roam.corp.google.com> <4d777ed8c17b479e59b16cc0b4e9a3f6537f9884.camel@kernel.crashing.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4d777ed8c17b479e59b16cc0b4e9a3f6537f9884.camel@kernel.crashing.org> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 20, 2018 at 12:10:59PM +1000, Benjamin Herrenschmidt wrote: > I chose to create a new mutex which we should be able to address other > similar races if we find them. The other solutions that I dismissed > were: > > - Using the device_lock. A explained previously, this is tricky, I > prefer not using this for anything other than locking against > concurrent add/remove. The main issue is that drivers will be sometimes > called in context where that's already held, so we can't take it inside > pci_enable_device() and I'd rather not add new constraints such as > "pci_enable_device() must be only called from probe() unless you also > take the device lock". It would be tricky to audit everybody... > > - Using a global mutex. We could move the bridge lock from AER to core > code for example, and use that. But it doesn't buy us much, and > slightly redecuces parallelism. It also makes it a little bit more > messy to walk up the bridge chain, we'd have to do a > pci_enable_device_unlocked or something, messy. +1 from my side for adding a struct mutex to struct pci_dev to protect state changes. The device_lock() primarily protects binding / unbinding of the device and pci_dev state may have to be changed while binding / unbinding. A global lock invites deadlocks if multiple devices are added / removed concurrently where one is a parent of the other. (Think hot-removal of multiple devices on a Thunderbolt daisy-chain.) As said I'd also welcome folding PCI_DEV_DISCONNECTED into enum pci_channel_state, either as an additional state or by using pci_channel_io_perm_failure. Thanks, Lukas