Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933741AbcKHUwE (ORCPT ); Tue, 8 Nov 2016 15:52:04 -0500 Received: from smtp.codeaurora.org ([198.145.29.96]:37572 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933370AbcKHUwD (ORCPT ); Tue, 8 Nov 2016 15:52:03 -0500 DMARC-Filter: OpenDMARC Filter v1.3.1 smtp.codeaurora.org E2404611C8 Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=pass smtp.mailfrom=skannan@codeaurora.org Message-ID: <58223AF1.2030605@codeaurora.org> Date: Tue, 08 Nov 2016 12:52:01 -0800 From: Saravana Kannan User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130329 Thunderbird/17.0.5 MIME-Version: 1.0 To: Chanwoo Choi 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> In-Reply-To: <5821948B.2010907@samsung.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2916 Lines: 71 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. -Saravana -- Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project