From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751977AbcKICgS (ORCPT ); Tue, 8 Nov 2016 21:36:18 -0500 Received: from mailout3.samsung.com ([203.254.224.33]:54147 "EHLO mailout3.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751100AbcKICgQ (ORCPT ); Tue, 8 Nov 2016 21:36:16 -0500 MIME-version: 1.0 Content-type: text/plain; charset=utf-8 X-AuditID: cbfee61a-f79916d0000062de-65-58228b9eb14f Content-transfer-encoding: 8BIT Message-id: <58228B9E.2090108@samsung.com> Date: Wed, 09 Nov 2016 11:36:14 +0900 From: Chanwoo Choi Organization: Samsung Electronics User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 To: Saravana Kannan Cc: "Rafael J. Wysocki" , MyungJoo Ham , Kyungmin Park , linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] PM / devfreq: Restart previous governor if new governor fails to start References: <1477509425-16936-1-git-send-email-skannan@codeaurora.org> <5820CE7E.40802@codeaurora.org> <5821948B.2010907@samsung.com> <58223AF1.2030605@codeaurora.org> <58227CDB.6050907@samsung.com> In-reply-to: <58227CDB.6050907@samsung.com> X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFtrCIsWRmVeSWpSXmKPExsVy+t9jQd153UoRBi92i1ucbXrDbnF51xw2 i8+9RxgtbjeuYLM4c/oSq8WBixPZHNg8Lvf1MnlsudrO4tG3ZRWjx+dNcgEsUW42GamJKalF Cql5yfkpmXnptkqhIW66FkoKeYm5qbZKEbq+IUFKCmWJOaVAnpEBGnBwDnAPVtK3S3DLOLD2 JHPBO7mKz7eOsTYwPpboYuTkkBAwkdixtZMVwhaTuHBvPVsXIxeHkMAsRomFTxaxgSR4BQQl fky+x9LFyMHBLCAvceRSNoSpLjFlSi5E+QNGiQWn/rNDlGtJTGleBGazCKhKrJ12hgnEZgOK 739xA2wkv4CixNUfjxlB5ogKREh0n6gECYsI6Ej8/XOdBWQms8BeRomlbyDmCAskSDS0HWOG WHaVSeL583dgCU4BbYkdEz+zTWAUnIXk1FkIp85COHUBI/MqRonUguSC4qT0XMO81HK94sTc 4tK8dL3k/NxNjOAYeya1g/HgLvdDjAIcjEo8vAceK0YIsSaWFVfmHmKU4GBWEuEN6FKKEOJN SaysSi3Kjy8qzUktPsRoCvTrRGYp0eR8YPznlcQbmpibmBsbWJhbWpoYKYnzNs5+Fi4kkJ5Y kpqdmlqQWgTTx8TBKdXA6GX07bXvAa3Yk6e95k+z/l8msnG3SVTaxqe7Z3YUrN9yUHZ2ddvM b837hY6cM/xYOk9cwbTat6Y+GRiU86RDxablpQQvTb3R1+qafN7v5IL0IsWOafNu/eHm/CW7 /LLHtxX1LfO+rlxg7nLgtOrhxGvO59Qu2LR8XcdyWfauQkJhxF4Zj+IMJZbijERDLeai4kQA IrzHRccCAAA= X-MTR: 20000000000000000@CPGS Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On 2016년 11월 09일 10:33, Chanwoo Choi wrote: > On 2016년 11월 09일 05:52, Saravana Kannan wrote: >> On 11/08/2016 01:02 AM, Chanwoo Choi wrote: >>> Hi, >>> >>> On 2016년 11월 08일 03:57, Saravana Kannan wrote: >>>> On 10/26/2016 05:06 PM, Chanwoo Choi wrote: >>>>> Hi, >>>>> >>>>> On 2016년 10월 27일 04:17, Saravana Kannan wrote: >>>>>> If the new governor fails to start, switch back to old governor so that the >>>>>> devfreq state is not left in some weird limbo. >>>>>> >>>>>> Signed-off-by: Saravana Kannan >>>>>> --- >>>>>> * Fix NULL deref for real this time. >>>>>> * Addressed some style preferences. >>>>>> >>>>>> drivers/devfreq/devfreq.c | 13 +++++++++++-- >>>>>> 1 file changed, 11 insertions(+), 2 deletions(-) >>>>>> >>>>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c >>>>>> index bf3ea76..77c41a5 100644 >>>>>> --- a/drivers/devfreq/devfreq.c >>>>>> +++ b/drivers/devfreq/devfreq.c >>>>>> @@ -919,7 +919,7 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr, >>>>>> struct devfreq *df = to_devfreq(dev); >>>>>> int ret; >>>>>> char str_governor[DEVFREQ_NAME_LEN + 1]; >>>>>> - struct devfreq_governor *governor; >>>>>> + const struct devfreq_governor *governor, *prev_governor; >>>>>> >>>>>> ret = sscanf(buf, "%" __stringify(DEVFREQ_NAME_LEN) "s", str_governor); >>>>>> if (ret != 1) >>>>>> @@ -944,12 +944,21 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr, >>>>>> goto out; >>>>>> } >>>>>> } >>>>>> + prev_governor = df->governor; >>>>>> df->governor = governor; >>>>>> strncpy(df->governor_name, governor->name, DEVFREQ_NAME_LEN); >>>>>> ret = df->governor->event_handler(df, DEVFREQ_GOV_START, NULL); >>>>>> - if (ret) >>>>>> + if (ret) { >>>>>> dev_warn(dev, "%s: Governor %s not started(%d)\n", >>>>>> __func__, df->governor->name, ret); >>>>>> + if (prev_governor) { >>>>> >>>>> I think that prev_governor is always set. You don't need to check it. >>>>> Why do check it? >>>> >>>> Not true. Even higher up in this function, we check if df->governor != NULL. Simple example would be that the default governor passed in while adding the device isn't compiled in. >>> >>> I don't understand. If device is not registered by devfreq_add_device(), >>> you don't change the governor by using governor_store(). >>> >>> If you can change the governor through governor_store(), >>> it means that the devfreq instance was added without any problem. >>> The added devfreq instance must have the sepecific governor >>> on df->governor variable. >>> >>> So, I think that df->governor is always set and then prev_governor is always set. >> >> Read the code more closely. add_device doesn't (and shouldn't) fail if the governor isn't present. After that, the governor could be changed from user space. > > If governor is not present during devfreq_add_device(), > the devfreq instance is not able to register the devfreq framework. > So, the user never touch the sysfs[1] to change the governor > because the sysfs[1] is not created by devfreq framework. > [1] /sys/class/devfreq/[device name]/governor > > In summary, if governor is not present during devfreq_add_device(), > the devfreq framework doesn't create tye sysfs[1] for governor. > > The user-space never change the governor through sysfs[1] > because there is no any sysfs entry[1]. I checked the code of devfreq_add_device(). As you mentioned, if there is no governor, devfreq_add_device() don't pass wihtout calling the devfreq->governor->even_handler(). I discussed this issue with Myungjoo Ham (devfreq maintainer). It is bug of devfreq_add_device(). I'll fix this issue. Best Regards, Chanwoo Choi