Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756672Ab3FSIbr (ORCPT ); Wed, 19 Jun 2013 04:31:47 -0400 Received: from na3sys009aog135.obsmtp.com ([74.125.149.84]:58035 "EHLO na3sys009aog135.obsmtp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755576Ab3FSIbo (ORCPT ); Wed, 19 Jun 2013 04:31:44 -0400 Message-ID: <51C16B97.3040304@marvell.com> Date: Wed, 19 Jun 2013 16:28:07 +0800 From: Xiaoguang Chen Organization: Marvell User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121011 Thunderbird/16.0.1 MIME-Version: 1.0 To: Viresh Kumar CC: "rjw@sisk.pl" , "cpufreq@vger.kernel.org" , "linux-pm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Ning Jiang , Zhoujie Wu , Yilu Mao , "chenxg.marvell@gmail.com" Subject: Re: [PATCH v9] Cpufreq: Fix governor start/stop race condition References: <1371625207-26702-1-git-send-email-chenxg@marvell.com> In-Reply-To: Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2217 Lines: 51 On 06/19/2013 03:55 PM, Viresh Kumar wrote: > On 19 June 2013 12:30, Xiaoguang Chen wrote: >> Cpufreq governor's stop and start operation should be kept in sequence. >> If not, there will be unexpected behavior, for example: >> >> There are 4 CPUs and policy->cpu=CPU0, CPU1/2/3 are linked to CPU0. >> The normal sequence is as below: >> >> 1) Current governor is userspace, One application tries to set >> governor to ondemand. It will call __cpufreq_set_policy in which it >> will stop userspace governor and then start ondemand governor. >> >> 2) Current governor is userspace, Now CPU0 hotplugs in CPU3 (put CPU3 online), >> It will call cpufreq_add_policy_cpu in which it first stops userspace >> governor, and then starts userspace governor. >> >> Now if the sequence of above two cases interleaves, It becomes like below: >> >> 1) Application stops userspace governor >> 2) Hotplug stops userspace governor >> 3) Application starts ondemand governor >> 4) Hotplug starts a governor >> >> In step 4, Hotplug is supposed to start userspace governor, But now >> the governor has been changed by application to ondemand, So hotplug >> starts ondemand governor again !!!! >> >> The solution is: Do not allow stop policy's governor multi-times. >> Governor should only be stopped once for one policy, After it is stopped, >> No other governor stop operation should be executed. also add one mutex to >> protect __cpufreq_governor so governor operation can be kept in sequence. >> >> Signed-off-by: Xiaoguang Chen >> Acked-by: Viresh Kumar >> --- >> drivers/cpufreq/cpufreq.c | 24 ++++++++++++++++++++++++ >> include/linux/cpufreq.h | 1 + >> 2 files changed, 25 insertions(+) > All good now. Sorry for the noise :) Thank you for the professional instructions. It makes the code more beautiful. :) -- Thanks Xiaoguang -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/