Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752129Ab3FXGEz (ORCPT ); Mon, 24 Jun 2013 02:04:55 -0400 Received: from mail-la0-f54.google.com ([209.85.215.54]:53920 "EHLO mail-la0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751115Ab3FXGEy (ORCPT ); Mon, 24 Jun 2013 02:04:54 -0400 MIME-Version: 1.0 In-Reply-To: <51C16B97.3040304@marvell.com> References: <1371625207-26702-1-git-send-email-chenxg@marvell.com> <51C16B97.3040304@marvell.com> Date: Mon, 24 Jun 2013 14:04:50 +0800 Message-ID: Subject: Re: [PATCH v9] Cpufreq: Fix governor start/stop race condition From: Xiaoguang Chen To: Xiaoguang Chen Cc: Viresh Kumar , "rjw@sisk.pl" , "cpufreq@vger.kernel.org" , "linux-pm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Ning Jiang , Zhoujie Wu , Yilu Mao 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: 2381 Lines: 62 Hi, Rafael When can this patch be merged? 2013/6/19 Xiaoguang Chen : > 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/