On 07/06/2015 11:01 AM, Shengjiu Wang wrote:
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"?
That will be up to the dmaengine driver. But it basically comes down to two things:
1) The driver needs to make sure that tasklet_schedule() is no longer called after terminate_all() has finished. 2) In the sync() callback call tasklet_kill() to make sure that it has finished running
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.
The sync() function will only wait if there is a callback scheduled, if there is non scheduled it will return immediately.