Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755190Ab3FLHKO (ORCPT ); Wed, 12 Jun 2013 03:10:14 -0400 Received: from mail-la0-f42.google.com ([209.85.215.42]:64516 "EHLO mail-la0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755037Ab3FLHKK (ORCPT ); Wed, 12 Jun 2013 03:10:10 -0400 MIME-Version: 1.0 In-Reply-To: References: <1370764205-3933-1-git-send-email-chenxg@marvell.com> Date: Wed, 12 Jun 2013 15:10:05 +0800 Message-ID: Subject: Re: [PATCH v2] 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: 4074 Lines: 101 2013/6/10 Viresh Kumar : > On 9 June 2013 13:20, 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 governor multi-times >> Governor stop should only do once, after it is stopped, >> no other governor stop should be executed. >> >> Signed-off-by: Xiaoguang Chen >> --- >> drivers/cpufreq/cpufreq.c | 10 +++++++++- >> include/linux/cpufreq.h | 1 + >> 2 files changed, 10 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c >> index 2d53f47..c8d7cb2 100644 >> --- a/drivers/cpufreq/cpufreq.c >> +++ b/drivers/cpufreq/cpufreq.c >> @@ -1562,6 +1562,11 @@ static int __cpufreq_governor(struct cpufreq_policy *policy, >> >> pr_debug("__cpufreq_governor for CPU %u, event %u\n", >> policy->cpu, event); >> + >> + if ((!policy->governor->enabled && (event == CPUFREQ_GOV_STOP)) || >> + (policy->governor->enabled && (event == CPUFREQ_GOV_START))) >> + return 0; >> + >> ret = policy->governor->governor(policy, event); >> >> if (!ret) { >> @@ -1569,6 +1574,10 @@ static int __cpufreq_governor(struct cpufreq_policy *policy, >> policy->governor->initialized++; >> else if (event == CPUFREQ_GOV_POLICY_EXIT) >> policy->governor->initialized--; >> + else if (event == CPUFREQ_GOV_STOP) >> + policy->governor->enabled = 0; >> + else if (event == CPUFREQ_GOV_START) >> + policy->governor->enabled = 1; >> } >> >> /* we keep one module reference alive for >> @@ -1581,7 +1590,6 @@ static int __cpufreq_governor(struct cpufreq_policy *policy, >> return ret; >> } >> >> - >> int cpufreq_register_governor(struct cpufreq_governor *governor) >> { >> int err; >> diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h >> index 037d36a..16c5b70 100644 >> --- a/include/linux/cpufreq.h >> +++ b/include/linux/cpufreq.h >> @@ -199,6 +199,7 @@ struct cpufreq_governor { >> will fallback to performance governor */ >> struct list_head governor_list; >> struct module *owner; >> + int enabled; >> }; > > This isn't sufficient. > > If there are two groups of clk-sharing-cpus, i.e. if we have multiple > policies and they are using same governor, then these functions > gets called twice for governor x. And you will return 0 for the second > policy. So this enable flag should be per policy, right? I'll modify this patch 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/