Does this really help, or just obfuscate the code?

What's the idea of these dummy acquire/release now?

I worry that some software may incorrectly parse this.

It is quite common to define macros when locking. I think it makes it more readable.

It's kind of like Read/Copy/Update lock.

If you look where sndstat_acquire is used:

pcm_unregister():
...
        PCM_LOCK(d);
        d->flags |= SD_F_DYING;
        d->flags &= ~SD_F_REGISTERED;
        PCM_UNLOCK(d);
...
sndstat_release();

The dummy lock/unlock ensures that next time someone reads the sound status it sees that the device is gone. Or if it was currently iterating that it waits for that.

I'll look into it a bit and see if there are any races left.

Yes, it's a risk. I checked some tools like pulseaudio() and they mostly look for pcm%d . I can check a bit more.