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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,UNPARSEABLE_RELAY 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 10BC3C43142 for ; Fri, 22 Jun 2018 17:14:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C247F24689 for ; Fri, 22 Jun 2018 17:14:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C247F24689 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=collabora.com 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 S933576AbeFVROH (ORCPT ); Fri, 22 Jun 2018 13:14:07 -0400 Received: from bhuna.collabora.co.uk ([46.235.227.227]:54898 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754497AbeFVROD (ORCPT ); Fri, 22 Jun 2018 13:14:03 -0400 Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: ezequiel) with ESMTPSA id B822C276E5D Message-ID: <1e792d3c972998f92109c127886243e32c4cde71.camel@collabora.com> Subject: Re: [PATCH v3] PM / devfreq: Fix devfreq_add_device() when drivers are built as modules. From: Ezequiel Garcia To: Akhil P Oommen , Enric Balletbo i Serra , linux-kernel@vger.kernel.org Cc: kernel@collabora.com, Chanwoo Choi , Kyungmin Park , MyungJoo Ham , linux-pm@vger.kernel.org Date: Fri, 22 Jun 2018 14:13:53 -0300 In-Reply-To: References: <20180621220430.25644-1-enric.balletbo@collabora.com> <0383b4a703a0b619023c0654a4a7637419c72ebd.camel@collabora.com> Organization: Collabora Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.2-1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hey Akhil, On Fri, 2018-06-22 at 12:33 +0530, Akhil P Oommen wrote: > On 6/22/2018 6:41 AM, Ezequiel Garcia wrote: > > Hey Enric, > > > > On Fri, 2018-06-22 at 00:04 +0200, Enric Balletbo i Serra wrote: > > > When the devfreq driver and the governor driver are built as > > > modules, > > > the call to devfreq_add_device() or governor_store() fails > > > because > > > the > > > governor driver is not loaded at the time the devfreq driver > > > loads. > > > The > > > devfreq driver has a build dependency on the governor but also > > > should > > > have a runtime dependency. We need to make sure that the governor > > > driver > > > is loaded before the devfreq driver. > > > > > > This patch fixes this bug by adding a try_then_request_governor() > > > function. First tries to find the governor, and then, if it is > > > not > > > found, > > > it requests the module and tries again. > > > > > > Fixes: 1b5c1be2c88e (PM / devfreq: map devfreq drivers to > > > governor > > > using name) > > > Signed-off-by: Enric Balletbo i Serra > > om> > > > --- > > > > > > Changes in v3: > > > - Remove unneded change in dev_err message. > > > - Fix err returned value in case to not find the governor. > > > > > > Changes in v2: > > > - Add a new function to request the module and call that function > > > from > > > devfreq_add_device and governor_store. > > > > > > drivers/devfreq/devfreq.c | 65 > > > ++++++++++++++++++++++++++++++++----- > > > -- > > > > [snip snip] > > > - governor = find_devfreq_governor(devfreq- > > > >governor_name); > > > + governor = try_then_request_governor(devfreq- > > > > governor_name); > > > > > > if (IS_ERR(governor)) { > > > dev_err(dev, "%s: Unable to find governor for > > > the > > > device\n", > > > __func__); > > > err = PTR_ERR(governor); > > > - goto err_init; > > > + goto err_unregister; > > > } > > > > > > + mutex_lock(&devfreq_list_lock); > > > + > > > > I know it's not something we are introducing in this patch, > > but still... calling a hook with a mutex held looks > > fishy to me. > > > > This lock should only protect the list, unless I am missing > > something. > > > > > devfreq->governor = governor; > > > err = devfreq->governor->event_handler(devfreq, > > > DEVFREQ_GOV_START, > > > NULL); > > > @@ -663,14 +703,16 @@ struct devfreq *devfreq_add_device(struct > > > device *dev, > > > __func__); > > > goto err_init; > > > } > > > + > > > + list_add(&devfreq->node, &devfreq_list); > > > + > > > mutex_unlock(&devfreq_list_lock); > > > > > > return devfreq; > > > > > > err_init: > > > - list_del(&devfreq->node); > > > mutex_unlock(&devfreq_list_lock); > > > - > > > +err_unregister: > > > device_unregister(&devfreq->dev); > > > err_dev: > > > if (devfreq) > > > @@ -988,12 +1030,13 @@ static ssize_t governor_store(struct > > > device > > > *dev, struct device_attribute *attr, > > > if (ret != 1) > > > return -EINVAL; > > > > > > - mutex_lock(&devfreq_list_lock); > > > - governor = find_devfreq_governor(str_governor); > > > + governor = try_then_request_governor(str_governor); > > > if (IS_ERR(governor)) { > > > - ret = PTR_ERR(governor); > > > - goto out; > > > + return PTR_ERR(governor); > > > } > > > + > > > + mutex_lock(&devfreq_list_lock); > > > + > > > if (df->governor == governor) { > > > ret = 0; > > > goto out; > > > -- > > > 2.17.1 > > > > > > > > > > Regards, > > Eze > > Adding to Ezequiel's point, shouldn't we take more granular lock > (devfreq->lock) first and then call devfreq_list_lock at the time of > adding to the list? > Not sure why we should do that. devfreq->lock should be used to protect the struct devfreq state, while the devfreq_list_lock is apparently protecting the two lists (which seem unrelated lists). So, the two locks are not correlated. Regards, Eze