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

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Date:	Thu, 15 Jan 2015 07:14:02 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	jiwang <jiada_wang@...tor.com>
Cc:	Fabio Estevam <festevam@...il.com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Mark Brown <broonie@...nel.org>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	"Frkuska, Joshua" <Joshua_Frkuska@...tor.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"lgirdwood@...il.com" <lgirdwood@...il.com>
Subject: Re: [alsa-devel] unload Audio drivers while playback stream is active case kernel crash

At Thu, 15 Jan 2015 13:40:49 +0900,
jiwang wrote:
> 
> Hi
> On 01/14/2015 10:43 PM, Fabio Estevam wrote:
> > On Wed, Jan 14, 2015 at 10:57 AM, Lars-Peter Clausen <lars@...afoo.de> wrote:
> >
> >> My personal opinion on this is that disallowing module removal while a
> >> driver registered by the module when is in use, while there is no technical
> >> reason to do so, is a anti-feature. Whether in ALSA or elsewhere.
> >>
> >> But looking at the source it seems that this is a core feature of ALSA and
> >> at least for the card module itself it will do the ref-counting when a
> >> stream is started/stopped. And we even support setting the owner of a card
> >> in ASoC. It's just that pretty much no ASoC card driver bothers to set the
> >> owner field in the snd_soc_card struct. So this particular problem can be
> >> fixed by updating the imx-wm8962 driver to set the owner field.
> > Thanks, Lars_Peter. This fixes the issue:
> >
> > root@...escale /$ modprobe -r snd_soc_imx_wm8962
> > modprobe: can't unload module snd_soc_imx_wm8962: Resource temporarily
> > unavailable
> >
> > Will send a patch with your suggestion soon.
> I think by set owner field in imx_wm8962 machine driver can fix the 
> crash I saw on sabreSD board,
> but as this is a generic issue which I suppose should exist on other 
> boards with different
> machine drivers.
> 
> Can we have a more generic fix to this issue?
> Or shall we set owner field for all machine drivers?

This is two folds.  The lack of card's owner field is a bug of each
driver.  Another is the missing of a hotplug-safe cleanup in ASoC
core.


Takashi
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