From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753522AbcKHJCL (ORCPT ); Tue, 8 Nov 2016 04:02:11 -0500 Received: from mailout1.samsung.com ([203.254.224.24]:43763 "EHLO mailout1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752600AbcKHJCH (ORCPT ); Tue, 8 Nov 2016 04:02:07 -0500 MIME-version: 1.0 Content-type: text/plain; charset=utf-8 X-AuditID: cbfee61a-f79916d0000062de-21-5821948be94e Content-transfer-encoding: 8BIT Message-id: <5821948B.2010907@samsung.com> Date: Tue, 08 Nov 2016 18:02:03 +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> In-reply-to: <5820CE7E.40802@codeaurora.org> X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFtrCIsWRmVeSWpSXmKPExsVy+t9jAd3uKYoRBs/6eS3ONr1ht7i8aw6b xefeI4wWtxtXsFmcOX2J1eLAxYlsDmwel/t6mTy2XG1n8ejbsorR4/MmuQCWKDebjNTElNQi hdS85PyUzLx0W6XQEDddCyWFvMTcVFulCF3fkCAlhbLEnFIgz8gADTg4B7gHK+nbJbhl/Dr1 kL3gn3DF+s2HWBsYH/B3MXJySAiYSEw9Mp0ZwhaTuHBvPVsXIxeHkMBSRoklq1eygCR4BQQl fky+B2RzcDALyEscuZQNYapLTJmSC1H+gFFi2sx3TBDlWhIzDt4Ga2URUJU4uOEsmM0GFN// 4gYbiM0voChx9cdjRpA5ogIREt0nKkHCIgI6En//XGcBmckssJdRYumbRewgCWGBBImGtmPM EMs+M0psn38TbBknUMfVmf2MExgFZyE5dRbCqbMQTl3AyLyKUSK1ILmgOCk91zAvtVyvODG3 uDQvXS85P3cTIzjGnkntYDy4y/0QowAHoxIPb4eMYoQQa2JZcWXuIUYJDmYlEd7eSUAh3pTE yqrUovz4otKc1OJDjKZAv05klhJNzgfGf15JvKGJuYm5sYGFuaWliZGSOG/j7GfhQgLpiSWp 2ampBalFMH1MHJxSDYx+ffIvH9XuzWo/bMe/flrOtxb79sdi54TLFF7Fpoh3tL97r2F1uK/m 4DRn1SVdX4Vex59eW/6o/lzF/OjSZ/5ek+2i/XeYPnw9ab9NTmrN25rvpkK39ZrEP8QYnlZY 8CRp9Ur/zH+5eifiWzjj9bbbzj9Qy3zEbvmka727Zx9dUzIn4opG5QwlluKMREMt5qLiRABZ ZoomxwIAAA== 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 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. Best Regards, Chanwoo Choi