On Tue, Jul 07, 2015 at 03:32:02PM +0200, Lars-Peter Clausen wrote: > On 07/07/2015 12:13 PM, Shengjiu Wang wrote: > >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. > > Most drivers can't make sure that the interrupt routine is not > executed after terminate_all() has been called, since both are fully > asynchronous. But what the driver needs to take care of is to > synchronize the two e.g. using a spin_lock() and make sure that if > terminate_all() has been called tasklet_schedule() is not called, > even if the isr is executed. Most drivers get this rigght. > > >>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? > > No, this is the way to go. You have two asynchronous processes and > you want to get deterministic execution ordering between the two you > need to add a synchronization primitive. > > - Lars > Thanks your advice. It is workable. But need to add new api in dmaengine.h I think about another method, can we add spin_lock in dmaengine_pcm_dma_complete() and snd_dmaengine_pcm_close()? and add a flag for pcm_close, if pcm closed, then just do nothing in dma complete. How do you think for this? 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
