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.
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().
Or move the most code of soc_cleanup_card_resources() to card->private_free or such to be called from snd_card_free(), and snd_soc_unregister_card() just needs to call snd_card_free(). This will trigger the disconnection, settle down the device usages then release the soc resources gracefully.
Takashi