Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753320AbbBBPFH (ORCPT ); Mon, 2 Feb 2015 10:05:07 -0500 Received: from aserp1040.oracle.com ([141.146.126.69]:33267 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751354AbbBBPFD (ORCPT ); Mon, 2 Feb 2015 10:05:03 -0500 Message-ID: <54CF9209.1050403@oracle.com> Date: Mon, 02 Feb 2015 23:04:41 +0800 From: ethan zhao Organization: Oracle Corporation User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20130107 Thunderbird/17.0.2 MIME-Version: 1.0 To: Viresh Kumar CC: Rafael Wysocki , santosh shilimkar , Linaro Kernel Mailman List , "linux-pm@vger.kernel.org" , linux-kernel Subject: Re: [PATCH Resend] cpufreq: Set cpufreq_cpu_data to NULL before putting kobject References: <54CEECF7.7020504@oracle.com> <54CEF123.5050106@oracle.com> <54CEF574.6040404@oracle.com> <54CEF7AA.80401@oracle.com> <54CEFA23.7040705@oracle.com> <54CF0106.5050601@oracle.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Source-IP: acsinet22.oracle.com [141.146.126.238] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2211 Lines: 52 On 2015/2/2 12:54, Viresh Kumar wrote: > On 2 February 2015 at 10:15, ethan zhao wrote: >> On 2015/2/2 12:26, Viresh Kumar wrote: >> But there is no checking against refcount in or before >> >> cpufreq_policy_free(), that is one issue I mentioned. > As I said earlier, the completion will only fire once the refcount > is zero. And so there is no need of any check here. > >>> That routines doesn't have any tricks and simply frees the policy. >>> Because, before calling cpufreq_policy_put_kobj(), we have set >>> the per-cpu variable to NULL, nobody else will get the policy >> It is possible cpufreq_cpu_get() within the PPC thread was called just >> before __cpufreq_remove_dev_finish() is to be called in another thread, >> so you set the per_cpu(cpufreq_cpu_data, cpu) to NULL will not prevent >> the actions between cpufreq_cpu_get and cpufreq_cpu_put(). >> >> And then the freeing happens in __cpufreq_remove_dev_finish(). > It will.. You aren't looking closely enough. If cpufreq_cpu_get() is called just > before remove-dev, then cpufreq_cpu_get() will take: > > read_lock_irqsave(&cpufreq_driver_lock, flags); > > And it will do: > > read_unlock_irqrestore(&cpufreq_driver_lock, flags); > > only after increasing the refcount with kobject_get(). > > While on the other side __cpufreq_remove_dev_finish() will do this: > > write_lock_irqsave(&cpufreq_driver_lock, flags); > policy = per_cpu(cpufreq_cpu_data, cpu); > per_cpu(cpufreq_cpu_data, cpu) = NULL; > write_unlock_irqrestore(&cpufreq_driver_lock, flags); > > So, it will wait for the read_lock in cpufreq_cpu_get() to finish before > setting per-cpu variable to NULL. And so, after kobject_put() in > cpufreq_policy_put_kobj(), we will wait for the completion to fire Closely enough this time, understood, thanks for your explanation. Ethan > and that will only happen once a corresponding cpufreq_cpu_put() > is issued. -- 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/