Re: [Qemu-devel] Intel HDA and ALSA audio driver hogging event loop

[P J P <ppandit@redhat.com>]

  Hello Gerd,

+-- On Thu, 20 Oct 2016, Stefan Hajnoczi wrote --+
| A RHEL 7.2 guest sometimes hangs when I play back a wav file on the
| Intel HDA emulated sound card using the QEMU ALSA audio driver.
| 
| intel_hda_xfer() transfers samples between the emulated card and the
| QEMU audio subsystem.  The following case causes a problem:
|     if (st->ctl & (1 << 26)) {
|         /*
|          * Wait with the next DMA xfer until the guest
|          * has acked the buffer completion interrupt
|          */
|         return false;
|     }
| 
| If the guest hasn't acked the interrupt yet then Intel HDA returns
| without providing any samples.  The QEMU ALSA driver keeps monitoring
| the file descriptor so the next event loop iteration will try to
| transfer samples again.

I was looking at another loop issue in 'intel_hda_xfer'
  -> https://lists.gnu.org/archive/html/qemu-devel/2016-10/msg04682.html

It does not address the above case, but maybe both could be fixed together.

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
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