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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