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

[Takashi Iwai <tiwai@suse.de>]

On Fri, 24 Sep 2021 21:24:13 +0200,
Pierre-Louis Bossart wrote:
> 
> 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.

Oh well, the missing piece was the lock inside the loop in
*_stream_assign().  It was lost while factoring out and converting to
the HD-audio core code.  (The lock wasn't taken on the whole loop at
that time because the list itself was supposed to be static.)

In anyway, I applied all patches except for patch#2, as the fixes for
spinlock look correct.


thanks,

Takashi