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

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Message-ID: <54B6679F.1030706@metafoo.de>
Date:	Wed, 14 Jan 2015 13:57:03 +0100
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Mark Brown <broonie@...nel.org>, Takashi Iwai <tiwai@...e.de>
CC:	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	"Wang, Jiada (ESD)" <Jiada_Wang@...tor.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"lgirdwood@...il.com" <lgirdwood@...il.com>,
	"Frkuska, Joshua" <Joshua_Frkuska@...tor.com>
Subject: Re: [alsa-devel] unload Audio drivers while playback stream is active
 case kernel crash

On 01/14/2015 01:02 PM, Mark Brown wrote:
[...]
>>> 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.
>
>> Well, the module unload means a more drastic cleanup.  Even if you
>> unbind, the code and data are still there while module unload may
>> clean them up all.
>
>> Above all, disallowing the module unload while using is the common
>> behavior of any other drivers.  Why do we have to be a rebel against
>> all civil manner? :)
>
> That's not true for everything and for ASoC I'd tend to assume that the
> user knows what they're doing and has a good reason for it; it's
> certainly something that can be helpful in development.


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.

- Lars

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