Messages in this thread | | | Date | Wed, 14 Jan 2015 11:00:47 +0100 | From | Lars-Peter Clausen <> | Subject | Re: [alsa-devel] unload Audio drivers while playback stream is active case kernel crash |
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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
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