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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0CE3FC433FE for ; Mon, 28 Nov 2022 17:28:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232144AbiK1R2P (ORCPT ); Mon, 28 Nov 2022 12:28:15 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43570 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232478AbiK1R2B (ORCPT ); Mon, 28 Nov 2022 12:28:01 -0500 Received: from mga17.intel.com (mga17.intel.com [192.55.52.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E76CA6444 for ; Mon, 28 Nov 2022 09:28:00 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1669656480; x=1701192480; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=wlocxIzZa2YAPiuBniHtUeU72dW8mhGyG945Z9QPseQ=; b=OA7aea87P+9Rd6sPCyg/7fPbpaSCPmmggCJq8R1gyPXY0lEG5TiEEoMx v2ThxvtcQ4qIZyOKFLT7ym+oUy+jF8BDoQJlNKlWIkEAFC5heEk6uvuQz Wj08p6xDqy0SVNzguDiMReJ4gr0D0RZYT4wHaVMWihKfN8PTjtWEk8w7Y +9IB/JWQwDQkLaHfWsxz3vX55MzQ8ELg2Q2hsruJfN4EZdf4cvtne9hZp vEhJl+NUD+00hrT+J1nAdrl449IqHEV7mH/giukNS+uvKtZpxFilB9vRy K+fiSnhBv0ZzKzE9Qn2ZzPL6GbNouH8RgaMNkFmPk/QPA/40zrRPKJspV g==; X-IronPort-AV: E=McAfee;i="6500,9779,10545"; a="295281628" X-IronPort-AV: E=Sophos;i="5.96,200,1665471600"; d="scan'208";a="295281628" Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Nov 2022 09:27:49 -0800 X-IronPort-AV: E=McAfee;i="6500,9779,10545"; a="888509534" X-IronPort-AV: E=Sophos;i="5.96,200,1665471600"; d="scan'208";a="888509534" Received: from kschjaer-mobl.amr.corp.intel.com (HELO [10.212.114.246]) ([10.212.114.246]) by fmsmga006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Nov 2022 09:27:48 -0800 Message-ID: <2d207a51-d415-726b-3bc1-8788df2f06fd@linux.intel.com> Date: Mon, 28 Nov 2022 11:18:02 -0600 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Firefox/102.0 Thunderbird/102.4.2 Subject: Re: [PATCH] soundwire: bus_type: Avoid lockdep assert in sdw_drv_probe() Content-Language: en-US To: Richard Fitzgerald , vkoul@kernel.org, yung-chuan.liao@linux.intel.com, sanyog.r.kale@intel.com Cc: patches@opensource.cirrus.com, alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org References: <20221121162453.1834170-1-rf@opensource.cirrus.com> From: Pierre-Louis Bossart In-Reply-To: <20221121162453.1834170-1-rf@opensource.cirrus.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/21/22 10:24, Richard Fitzgerald wrote: > Don't hold sdw_dev_lock while calling the peripheral driver > probe() and remove() callbacks. > > Holding sdw_dev_lock around the probe() and remove() calls > causes a theoretical mutex inversion which lockdep will > assert on. The peripheral driver probe will probably register > a soundcard, which will take ALSA and ASoC locks. During It's extremely unlikely that a peripheral driver would register a sound card, this is what machine drivers do. Which leads me to the question: is this a real problem? Or did you mean 'register components', and if yes what would the problem with lockdep be? > normal operation a runtime resume suspend can be triggered > while these locks are held and will then take sdw_dev_lock. > > It's not necessary to hold sdw_dev_lock when calling the > probe() and remove(), it is only used to prevent the bus core > calling the driver callbacks if there isn't a driver or the > driver is removing. > If sdw_dev_lock is held while setting and clearing the > 'probed' flag this is sufficient to guarantee the safety of > callback functions. not really, the 'probed' flag was kept for convenience. what this lock really protects is the dereferencing of ops after the driver .remove happens. > The potential race of a bus event happening while probe() is > executing is the same as the existing race of the bus event > handler taking the mutex first and processing the event > before probe() can run. In both cases the event has already > happened before the driver is probed and ready to accept > callbacks. Sorry, I wasn't able to parse the first sentence in this paragraph. what 'existing race' are you referring to? > > Signed-off-by: Richard Fitzgerald > --- > drivers/soundwire/bus_type.c | 9 +++------ > 1 file changed, 3 insertions(+), 6 deletions(-) > > diff --git a/drivers/soundwire/bus_type.c b/drivers/soundwire/bus_type.c > index 04b3529f8929..963498db0fd2 100644 > --- a/drivers/soundwire/bus_type.c > +++ b/drivers/soundwire/bus_type.c > @@ -105,20 +105,19 @@ static int sdw_drv_probe(struct device *dev) > if (ret) > return ret; > > - mutex_lock(&slave->sdw_dev_lock); > - > ret = drv->probe(slave, id); > if (ret) { > name = drv->name; > if (!name) > name = drv->driver.name; > - mutex_unlock(&slave->sdw_dev_lock); > > dev_err(dev, "Probe of %s failed: %d\n", name, ret); > dev_pm_domain_detach(dev, false); > return ret; > } > > + mutex_lock(&slave->sdw_dev_lock); > + > /* device is probed so let's read the properties now */ > if (drv->ops && drv->ops->read_prop) > drv->ops->read_prop(slave); > @@ -167,14 +166,12 @@ static int sdw_drv_remove(struct device *dev) > int ret = 0; > > mutex_lock(&slave->sdw_dev_lock); > - > slave->probed = false; > + mutex_unlock(&slave->sdw_dev_lock); > > if (drv->remove) > ret = drv->remove(slave); > > - mutex_unlock(&slave->sdw_dev_lock); > - > dev_pm_domain_detach(dev, false); > > return ret;