From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753895AbbANKAx (ORCPT ); Wed, 14 Jan 2015 05:00:53 -0500 Received: from smtp-out-243.synserver.de ([212.40.185.243]:1062 "EHLO smtp-out-243.synserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751112AbbANKAu (ORCPT ); Wed, 14 Jan 2015 05:00:50 -0500 X-SynServer-TrustedSrc: 1 X-SynServer-AuthUser: lars@metafoo.de X-SynServer-PPID: 17920 Message-ID: <54B63E4F.2010506@metafoo.de> Date: Wed, 14 Jan 2015 11:00:47 +0100 From: Lars-Peter Clausen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.3.0 MIME-Version: 1.0 To: Takashi Iwai CC: Mark Brown , "alsa-devel@alsa-project.org" , "Wang, Jiada (ESD)" , "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: 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 On 01/14/2015 09:47 AM, Takashi Iwai wrote: > At Wed, 14 Jan 2015 09:15:36 +0100, > 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. > > OK, so it's not about active stream. From the reporter's description, > I supposed that the module gets unloaded while playing a stream, which > shouldn't be allowed. Well one of the ways to trigger this is to remove the module while the stream is active. But it is not exclusively a problem module unload problem. E.g. the same happens if you hot-unplug the ASoC card. I don't think that we need to prevent module unload when a stream is active. From a framework point of view is not different from hot-unplug. I don't see a reason why we'd jump through hoops to actively forbid removing the module once it works just fine. - Lars