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=-12.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,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 0130DC432BE for ; Wed, 18 Aug 2021 14:51:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E0C316108E for ; Wed, 18 Aug 2021 14:51:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239554AbhHROwb (ORCPT ); Wed, 18 Aug 2021 10:52:31 -0400 Received: from mga17.intel.com ([192.55.52.151]:1553 "EHLO mga17.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239503AbhHROwa (ORCPT ); Wed, 18 Aug 2021 10:52:30 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10080"; a="196596161" X-IronPort-AV: E=Sophos;i="5.84,330,1620716400"; d="scan'208";a="196596161" Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Aug 2021 07:51:55 -0700 X-IronPort-AV: E=Sophos;i="5.84,330,1620716400"; d="scan'208";a="449785281" Received: from ksawchu-mobl.amr.corp.intel.com (HELO [10.212.83.236]) ([10.212.83.236]) by fmsmga007-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Aug 2021 07:51:53 -0700 Subject: Re: [RFC PATCH 1/2] driver core: export driver_deferred_probe_trigger() To: Mark Brown , Greg Kroah-Hartman Cc: alsa-devel@alsa-project.org, "Rafael J . Wysocki" , tiwai@suse.de, linux-kernel@vger.kernel.org, liam.r.girdwood@linux.intel.com, vkoul@kernel.org, Geert Uytterhoeven , Jason Gunthorpe , Dan Williams , Andy Shevchenko , Christoph Hellwig References: <20210817190057.255264-1-pierre-louis.bossart@linux.intel.com> <20210817190057.255264-2-pierre-louis.bossart@linux.intel.com> <20210818115736.GA4177@sirena.org.uk> <20210818134814.GF4177@sirena.org.uk> From: Pierre-Louis Bossart Message-ID: <14235b8d-d375-6e2d-cae9-33adf9c48120@linux.intel.com> Date: Wed, 18 Aug 2021 09:51:51 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Firefox/78.0 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210818134814.GF4177@sirena.org.uk> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >>> The issue is that the driver core is using drivers completing probe as a >>> proxy for resources becoming available. That works most of the time >>> because most probes are fully synchronous but it breaks down if a >>> resource provider registers resources outside of probe, we might still >>> be fine if system boot is still happening and something else probes but >>> only through luck. > >> The driver core is not using that as a proxy, that is up to the driver >> itself or not. All probe means is "yes, this driver binds to this >> device, thank you!" for that specific bus/class type. That's all, if >> the driver needs to go off and do real work before it can properly >> control the device, wonderful, have it go and do that async. > > Right, which is what is happening here - but the deferred probe > machinery in the core is reading more into the probe succeeding than it > should. I think Greg was referring to the use of the PROBE_PREFER_ASYNCHRONOUS probe type. We tried just that and got a nice WARN_ON because we are using request_module() to deal with HDaudio codecs. The details are in [1] but the kernel code is unambiguous... /* * We don't allow synchronous module loading from async. Module * init may invoke async_synchronize_full() which will end up * waiting for this task which already is waiting for the module * loading to complete, leading to a deadlock. */ WARN_ON_ONCE(wait && current_is_async()); The reason why we use a workqueue is because we are otherwise painted in a corner by conflicting requirements. a) we have to use request_module() b) we cannot use the async probe because of the request_module() c) we have to avoid blocking on boot I understand the resistance to exporting this function, no one in our team was really happy about it, but no one could find an alternate solution. If there is something better, I am all ears. Thanks -Pierre [1] https://github.com/thesofproject/linux/pull/3079