From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752234AbbANIZn (ORCPT ); Wed, 14 Jan 2015 03:25:43 -0500 Received: from relay1.mentorg.com ([192.94.38.131]:59044 "EHLO relay1.mentorg.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751759AbbANIZ0 (ORCPT ); Wed, 14 Jan 2015 03:25:26 -0500 Message-ID: <54B627F0.90207@mentor.com> Date: Wed, 14 Jan 2015 17:25:20 +0900 From: jiwang User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: Lars-Peter Clausen , Takashi Iwai , Mark Brown CC: "alsa-devel@alsa-project.org" , "linux-kernel@vger.kernel.org" , "lgirdwood@gmail.com" , "Frkuska, Joshua" Subject: Re: [alsa-devel] unload Audio drivers while playback stream is active case kernel crash References: <857E9EDCA6C0904DB3357321AA9123EB0108B66919@NA-MBX-01.mgc.mentorg.com> <20150113215412.GS4160@sirena.org.uk> <54B625A8.8090406@metafoo.de> In-Reply-To: <54B625A8.8090406@metafoo.de> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi On 01/14/2015 05:15 PM, Lars-Peter Clausen wrote: > On 01/14/2015 08:43 AM, Takashi Iwai wrote: >> At Tue, 13 Jan 2015 21:54:12 +0000, >> Mark Brown wrote: >>> >>> On Tue, Jan 13, 2015 at 06:24:44PM +0100, Takashi Iwai wrote: >>>> Wang, Jiada (ESD) wrote: >>> >>>>> I am using i.MX6Q sabreSD board, which have imx_wm892 machine >>>>> driver, wm8962 codec and SSI CPU DAI, >>> >>>>> I got Kernel crash when unloading audio drivers (playback stream >>>>> is active) >>>>> modprobe -r snd_soc_imx_wm8962 >>>>> modprobe -r snd_soc_fsl_ssi >>>>> modprobe -r snd_soc_wm8962 >>> >>>> The root problem is that you can unload the module while playing. >>>> The corresponding module refcounts should have been increased during >>>> used. >>> >>>> Do we miss [try_]module_get() somewhere in ASoC? >>> >>> That doesn't help, users can still forcibly unbind the driver at >>> runtime >>> without loading the module - and there's always the potential for >>> actually hotpluggable hardware. The teardown paths should be able to >>> cope somewhat gracefully. >> >> The module refcount has to be handled while being used for stopping >> module unload. That's irrelevant from the dynamic unbinding support >> itself. Of course, the module refcount doesn't save the world, but >> it's the right fix for this particular scenario. > > Refcounting won't help in this case. The issue is caused by a delayed > work item that gets launched when the PCM stream is stopped. So if you > decrease the refcount when the stream is stopped you still have a > window where it is possible to remove the module while the work is > still being scheduled. > > And while we do flush the scheduled work when we remove the ASoC card > this is done before snd_card_free() is called. So when snd_card_free() > is called it gets re-scheduled again. I think the correct fix is to > add a snd_card_disconnect() at the very top of > soc_cleanup_card_resources(). > when stream is active, snd_card_disconnect() will trigger pcm_close() be executed by another thread, we can't ensure the pcm_close() is executed before the rest of soc_cleanup_card_resources(). - Jiada > - Lars