From mboxrd@z Thu Jan 1 00:00:00 1970 From: ethan zhao Subject: Re: [PATCH Resend] cpufreq: Set cpufreq_cpu_data to NULL before putting kobject Date: Mon, 02 Feb 2015 11:56:36 +0800 Message-ID: <54CEF574.6040404@oracle.com> References: <54CEECF7.7020504@oracle.com> <54CEF123.5050106@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from aserp1040.oracle.com ([141.146.126.69]:51693 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932070AbbBBD44 (ORCPT ); Sun, 1 Feb 2015 22:56:56 -0500 In-Reply-To: Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Viresh Kumar Cc: Rafael Wysocki , santosh shilimkar , Linaro Kernel Mailman List , "linux-pm@vger.kernel.org" , linux-kernel On 2015/2/2 11:43, Viresh Kumar wrote: > On 2 February 2015 at 09:08, ethan zhao wrote: >>> We take cpufreq_driver_lock() here, and so this will >>> block thread B. >> No, there is no cpufreq_driver_lock acquired between >> >> cpufreq_cpu_get() and cpufreq_cpu_put() > I am not saying that the lock is taken between them. But within > cpufreq_cpu_get() to make sure policy doesn't get freed while we > are doing kobject_get(). How to prevent the policy to be freed between cpufreq_cpu_get() and cpufreq_cpu_put() ? >>>> beginning the deference of policy Thread B: >>>> ... ... __cpufreq_remove_dev_finish() >>>> cpufreq_policy_free(policy); >>>> >>>> >>>> Perhaps move policy->rwsem out side the policy structure is a way to >>>> avoid >>>> it completely. >>>> and you could stopping the PPC thread stepping forward as my patch as >>>> temporary workaround. >>> I couldn't understand your problem completely. Apart from giving a >>> detailed >>> look of what's going on both threads, always specify where the BUG >>> actually >>> is.. >> The problem is you are using a rwsem inside policy structure to protect its >> assessment, that is bad design. > What is the current bug you are facing right now, I haven't understood it well. > Also a lock within the structure isn't new. Its all over the kernel. I > don't understand > why you say its a bad design. You are maxing up the water with sand ? Thanks, Ethan > > -- > viresh