Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758597Ab3FMKDR (ORCPT ); Thu, 13 Jun 2013 06:03:17 -0400 Received: from mail-lb0-f176.google.com ([209.85.217.176]:40497 "EHLO mail-lb0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758566Ab3FMKDP (ORCPT ); Thu, 13 Jun 2013 06:03:15 -0400 MIME-Version: 1.0 In-Reply-To: References: <1371114118-19488-1-git-send-email-chenxg@marvell.com> Date: Thu, 13 Jun 2013 18:03:12 +0800 Message-ID: Subject: Re: [PATCH v5] cpufreq: fix governor start/stop race condition From: Xiaoguang Chen To: Viresh Kumar Cc: Xiaoguang Chen , "Rafael J. Wysocki" , cpufreq@vger.kernel.org, linux-pm@vger.kernel.org, "linux-kernel@vger.kernel.org" , njiang1@marvell.com, zjwu@marvell.com, ylmao@marvell.com Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2191 Lines: 53 2013/6/13 Viresh Kumar : > On 13 June 2013 14:31, Xiaoguang Chen wrote: >> cpufreq governor stop and start should be kept in sequence. >> If not, there will be unexpected behavior, for example: >> >> we have 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, it will >> call cpufreq_add_policy_cpu. on which it first stops userspace >> governor, and then starts userspace governor. >> >> Now if the sequence of above two cases interleaves, it becames >> below sequence: >> >> 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 one policy's governor multi-times >> Governor stop should only do once for one policy, after it is stopped, >> no other governor stop should be executed. also add one mutext to >> protect __cpufreq_governor so governor operation can be kept in sequence. >> >> Signed-off-by: Xiaoguang Chen >> --- >> drivers/cpufreq/cpufreq.c | 24 ++++++++++++++++++++++++ >> include/linux/cpufreq.h | 1 + >> 2 files changed, 25 insertions(+) > > I forgot to tell you earlier but please update changelog everytime you > send a new version. > > Acked-by: Viresh Kumar Thanks I'll pay attention next time :) 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/