[RFC PATCH 0/4] ALSA: hda: potential hdac_stream locking issues?

[Pierre-Louis Bossart]

While reviewing the HDAudio DMA handling, I found a number of
inconsistencies in how spin_locks are used. It's not clear what the
HDaudio bus->reg_lock is supposed to protect. In most cases only the
writes to specific boolean status flags are protected, and there are
multiple cases of taking the lock after testing a status flag.

This patchset suggests a more consistent locking pattern, but it's
entirely possible that the bus->reg_lock is only intented to protect
register read/write access on the HDaudio bus, and not the status
flags, and that this entire piece of code is completely
over-engineered.

On the Intel side no one knows why this spinlock was used, the reasons
are lost to history. I set the 'RFC' status on purpose in the hope
that Takashi might recall what this lock is supposed to protect. The
diff format makes this patchset difficult to review, it's recommended
to apply the patches and look at entire functions with changes to get
a better idea of the suggested changes.

Pierre-Louis Bossart (4):
  ALSA: hda: hdac_stream: fix potential locking issue in
    snd_hdac_stream_assign()
  ALSA: hda: hdac_stream: reset assigned_key in stream_release()
  ALSA: hda: hdac_ext_stream: fix potential locking issues
  ASoC: SOF: Intel: hda-dai: fix potential locking issue

 include/sound/hdaudio_ext.h     |  2 ++
 sound/hda/ext/hdac_ext_stream.c | 46 ++++++++++++++++++++-------------
 sound/hda/hdac_stream.c         |  5 ++--
 sound/soc/sof/intel/hda-dai.c   |  7 ++---
 4 files changed, 37 insertions(+), 23 deletions(-)

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2.25.1