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 11:38:11 +0800 Message-ID: <54CEF123.5050106@oracle.com> References: <54CEECF7.7020504@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Viresh Kumar Cc: Rafael Wysocki , santosh shilimkar , Linaro Kernel Mailman List , "linux-pm@vger.kernel.org" , linux-kernel List-Id: linux-pm@vger.kernel.org On 2015/2/2 11:24, Viresh Kumar wrote: > On 2 February 2015 at 08:50, ethan zhao wrote: >> This seems couldn't prevent all the 'bad thing' from happening, E.G. >> >> >> Thread A: Workqueue: kacpi_notify >> >> acpi_processor_notify() >> acpi_processor_ppc_has_changed() >> cpufreq_update_policy() >> cpufreq_cpu_get() > 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() >> 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. Thanks, Ethan