Messages in this thread | | | Date | Wed, 14 Jan 2015 10:34:32 +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 09:25 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
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