On Mon, Jul 06, 2015 at 02:27:01PM +0200, Lars-Peter Clausen wrote: > 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. Some driver can't make sure this. The dma interrupt may come later after terminate_all. > 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. Do you have other method to resolve this issue? or simple method? Best regards wang shengjiu -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
