From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754805AbaJ2Cpl (ORCPT ); Tue, 28 Oct 2014 22:45:41 -0400 Received: from out2-smtp.messagingengine.com ([66.111.4.26]:36791 "EHLO out2-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752943AbaJ2Cpj (ORCPT ); Tue, 28 Oct 2014 22:45:39 -0400 X-Sasl-enc: 57qi2Av11V81II/RyyxoD9mF+XV3B0stg04clQvpF38Q 1414550738 Date: Wed, 29 Oct 2014 10:44:26 +0800 From: Greg KH To: Tomeu Vizoso Cc: linux-kernel@vger.kernel.org, Javier Martinez Canillas , "Rafael J. Wysocki" , Viresh Kumar , linux-pm@vger.kernel.org Subject: Re: [PATCH 2/2] cpufreq: Guard against not-yet-initialized policies in cpufreq_cpu_get Message-ID: <20141029024426.GA7468@kroah.com> References: <1414510008-7262-1-git-send-email-tomeu.vizoso@collabora.com> <1414510008-7262-2-git-send-email-tomeu.vizoso@collabora.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1414510008-7262-2-git-send-email-tomeu.vizoso@collabora.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 28, 2014 at 04:26:48PM +0100, Tomeu Vizoso wrote: > There's a substantial window of opportunity from the time the policy objects > are created until they are initialized, causing this: > > [ 4.651435] ------------[ cut here ]------------ > [ 4.651453] WARNING: CPU: 1 PID: 64 at include/linux/kref.h:47 kobject_get+0x64/0x70() > [ 4.651463] Modules linked in: > [ 4.651473] CPU: 1 PID: 64 Comm: irq/77-tegra-ac Not tainted 3.18.0-rc1-next-20141027ccu-00049-g21a0041 #248 > [ 4.651497] [] (unwind_backtrace) from [] (show_stack+0x10/0x14) > [ 4.651505] [] (show_stack) from [] (dump_stack+0x98/0xd8) > [ 4.651515] [] (dump_stack) from [] (warn_slowpath_common+0x70/0x8c) > [ 4.651522] [] (warn_slowpath_common) from [] (warn_slowpath_null+0x1c/0x24) > [ 4.651530] [] (warn_slowpath_null) from [] (kobject_get+0x64/0x70) > [ 4.651539] [] (kobject_get) from [] (cpufreq_cpu_get+0x88/0xc8) > [ 4.651547] [] (cpufreq_cpu_get) from [] (cpufreq_get+0xc/0x64) > [ 4.651555] [] (cpufreq_get) from [] (actmon_thread_isr+0x140/0x1a4) > [ 4.651563] [] (actmon_thread_isr) from [] (irq_thread_fn+0x1c/0x40) > [ 4.651570] [] (irq_thread_fn) from [] (irq_thread+0x134/0x174) > [ 4.651579] [] (irq_thread) from [] (kthread+0xdc/0xf4) > [ 4.651587] [] (kthread) from [] (ret_from_fork+0x14/0x3c) > [ 4.651591] ---[ end trace 7f6a15d1272e6ef3 ]--- > > This commit checks that the policy object has been initialized already before > trying to ref it. > > Signed-off-by: Tomeu Vizoso > --- > drivers/cpufreq/cpufreq.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > index 644b54e..37cd6c9 100644 > --- a/drivers/cpufreq/cpufreq.c > +++ b/drivers/cpufreq/cpufreq.c > @@ -214,8 +214,12 @@ struct cpufreq_policy *cpufreq_cpu_get(unsigned int cpu) > if (cpufreq_driver) { > /* get the CPU */ > policy = per_cpu(cpufreq_cpu_data, cpu); > - if (policy) > - kobject_get(&policy->kobj); > + if (policy) { > + if (!kobject_initialized(&policy->kobj)) > + policy = NULL; > + else > + kobject_get(&policy->kobj); > + } Something else is going on here, sorry, this isn't the correct fix, as you are using kobjects incorrectly if this ever happens... thanks, greg k-h