linux-kernel - Re: [alsa-devel] unload Audio drivers while playback stream is active case kernel crash

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Date:	Wed, 14 Jan 2015 08:43:45 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Mark Brown <broonie@...nel.org>
Cc:	"Wang, Jiada (ESD)" <Jiada_Wang@...tor.com>,
	"lgirdwood@...il.com" <lgirdwood@...il.com>,
	"perex@...ex.cz" <perex@...ex.cz>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Frkuska, Joshua" <Joshua_Frkuska@...tor.com>
Subject: Re: [alsa-devel] unload Audio drivers while playback stream is active case kernel crash

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.


Takashi
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