From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lars-Peter Clausen Subject: Re: unload Audio drivers while playback stream is active case kernel crash Date: Wed, 14 Jan 2015 10:34:32 +0100 Message-ID: <54B63828.6030408@metafoo.de> References: <857E9EDCA6C0904DB3357321AA9123EB0108B66919@NA-MBX-01.mgc.mentorg.com> <20150113215412.GS4160@sirena.org.uk> <54B625A8.8090406@metafoo.de> <54B627F0.90207@mentor.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: Received: from smtp-out-243.synserver.de (smtp-out-243.synserver.de [212.40.185.243]) by alsa0.perex.cz (Postfix) with ESMTP id 545AE2608EA for ; Wed, 14 Jan 2015 10:34:33 +0100 (CET) In-Reply-To: <54B627F0.90207@mentor.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: alsa-devel-bounces@alsa-project.org To: jiwang , Takashi Iwai , Mark Brown Cc: "alsa-devel@alsa-project.org" , "Frkuska, Joshua" , "linux-kernel@vger.kernel.org" , "lgirdwood@gmail.com" List-Id: alsa-devel@alsa-project.org On 01/14/2015 09:25 AM, jiwang wrote: > 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(). Hm right, because that only gets called once the userspace application finally closes the PCM device. Takashi approach with moving things to the card_free callback might work better. - Lars