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=-0.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,UNPARSEABLE_RELAY,URIBL_BLOCKED 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 5BFAFC43143 for ; Fri, 22 Jun 2018 01:11:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1419323ABF for ; Fri, 22 Jun 2018 01:11:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1419323ABF 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 S934094AbeFVBLs (ORCPT ); Thu, 21 Jun 2018 21:11:48 -0400 Received: from bhuna.collabora.co.uk ([46.235.227.227]:50934 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933129AbeFVBLq (ORCPT ); Thu, 21 Jun 2018 21:11:46 -0400 Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: ezequiel) with ESMTPSA id D852C28952E Message-ID: <0383b4a703a0b619023c0654a4a7637419c72ebd.camel@collabora.com> Subject: Re: [PATCH v3] PM / devfreq: Fix devfreq_add_device() when drivers are built as modules. From: Ezequiel Garcia To: 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: Thu, 21 Jun 2018 22:11:36 -0300 In-Reply-To: <20180621220430.25644-1-enric.balletbo@collabora.com> References: <20180621220430.25644-1-enric.balletbo@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 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 > --- > > 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