Messages in this thread | | | Date | Wed, 14 Jan 2015 17:25:20 +0900 | From | jiwang <> | Subject | Re: [alsa-devel] unload Audio drivers while playback stream is active case kernel crash |
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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().
- Jiada
> - Lars
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