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Re: [PATCH 4/4] ALSA: pcm_dmaengine: Properly synchronize DMA on shutdown

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On Tue, 20 Oct 2015 13:40:00 +0200,
Lars-Peter Clausen wrote:
> 
> On 10/20/2015 01:17 PM, Takashi Iwai wrote:
> > On Tue, 20 Oct 2015 11:46:31 +0200,
> > Lars-Peter Clausen wrote:
> >>
> >> Use the new dmaengine_synchronize() function to make sure that all complete
> >> callbacks have finished running before the runtime data, which is accessed
> >> in the completed callback, is freed.
> >>
> >> This fixes a long standing use-after-free race condition that has been
> >> observed on some systems.
> > 
> > What if a substream is restarted immediately after the stop?
> > 
> 
> What can happen is that you get a complete callback and the associated
> snd_pcm_period_elapsed() too early, before the period has actually elapsed,
> but I don't think that this is a problem if the DMA driver properly
> implements residue reporting.
> 
> This fails if we rely on period counting, but that is broken anyway and
> already prone to other race conditions.
> 
> I've tested this series with xrun injection and some modifications to the
> DMA driver to always trigger the race condition when the stream is stopped.
> And I've not seen any issues after the transfer re-started. (There is a
> dead-lock condition though but that does not seem to be related to this series)

OK, then I'm fine with the changes.

I suppose this will go through dmaengine tree?  If so, feel free to
take my ack:
  Reviewed-by: Takashi Iwai <tiwai@suse.de>


thanks,

Takashi
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[PATCH 0/4] dmaengine: Add transfer termination synchronization support Lars-Peter Clausen <lars@metafoo.de> - 2015-10-20 11:50 +0200
  [PATCH 4/4] ALSA: pcm_dmaengine: Properly synchronize DMA on shutdown Lars-Peter Clausen <lars@metafoo.de> - 2015-10-20 11:50 +0200
    Re: [PATCH 4/4] ALSA: pcm_dmaengine: Properly synchronize DMA on shutdown Takashi Iwai <tiwai@suse.de> - 2015-10-20 13:20 +0200
      Re: [PATCH 4/4] ALSA: pcm_dmaengine: Properly synchronize DMA on  shutdown Lars-Peter Clausen <lars@metafoo.de> - 2015-10-20 13:50 +0200
        Re: [PATCH 4/4] ALSA: pcm_dmaengine: Properly synchronize DMA on shutdown Takashi Iwai <tiwai@suse.de> - 2015-10-20 14:40 +0200
        Re: [PATCH 4/4] ALSA: pcm_dmaengine: Properly synchronize DMA on  shutdown Lars-Peter Clausen <lars@metafoo.de> - 2015-10-20 15:10 +0200
  [PATCH 2/4] dmaengine: virt-dma: Add synchronization helper function Lars-Peter Clausen <lars@metafoo.de> - 2015-10-20 11:50 +0200
  [PATCH 1/4] dmaengine: Add transfer termination synchronization support Lars-Peter Clausen <lars@metafoo.de> - 2015-10-20 11:50 +0200
    Re: [PATCH 1/4] dmaengine: Add transfer termination synchronization support Andy Shevchenko <andy.shevchenko@gmail.com> - 2015-10-29 23:10 +0100
      Re: [PATCH 1/4] dmaengine: Add transfer termination synchronization  support Lars-Peter Clausen <lars@metafoo.de> - 2015-10-30 15:20 +0100
  [PATCH 3/4] dmaengine: axi_dmac: Add synchronization support Lars-Peter Clausen <lars@metafoo.de> - 2015-10-20 11:50 +0200
  Re: [PATCH 0/4] dmaengine: Add transfer termination synchronization  support Vinod Koul <vinod.koul@intel.com> - 2015-10-29 02:30 +0100

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