[alsa-devel] Issue in alsa when dma complete race with pcm release

[Shengjiu Wang]

On Fri, Jul 03, 2015 at 12:56:53PM +0200, Lars-Peter Clausen wrote:
> On 07/03/2015 10:25 AM, Shengjiu Wang wrote:
> >Hi alsa-devel
> >
> >    There maybe a issue in ALSA when dma complete race with snd_pcm_release.
> >The pcm release and dma complete are in different thread. There is occasion
> >that dmaengine_pcm_dma_complete() is called too late, some memory has been
> >freed, the prtd is null. Then there is kernel dump.
> >
> >    Is there any solution for this issue? Thanks.
> 
> We need to introduce a synchronization primitive that allows a
> dmaengine client to synchronize to the execution of the complete
> callbacks.
> 
> terminate_all() unfortunately can't do this since terminate_all()
> might be called from within one of the complete callbacks and so
> would cause a deadlock if we'd wait for all complete callbacks to
> finish before terminate_all() returns.
> 
> So what is needed is a new function called dmaengine_sync() that
> will wait until all scheduled complete callbacks have finished. A
> call to this function needs to be put in snd_dmaengine_pcm_close()
> before the prtd is closed.
> 
> - Lars

How to check " all scheduled complete callbacks have finished"?

One concern is if add wait in snd_dmaengine_pcm_close(), which wil cause 
the snd_pcm_release is bound with dmaengine, when there is error in dma
and no callback be called. Then the snd_pcm_release will not be released.


Best regards
wang shengjiu