[alsa-devel] Duplicate wake-ups in pcm_lib.c

[pl bossart]

>> I couldn't figure out who generates this null event, and even better
>> it does not show in the report printed by my test app. I am somewhat
>> lost here as to how snd_pcm_playback_poll works.
>
> Note that do_poll() in linux/fs/select.c first checks all given fds
> if there's an event. So probably the userspace just called poll() for a
> reason in different timing than sound one (processing event from another fd
> or so). I believe it's normal behaviour.

This was tested with alsa-lib/test/pcm.c; there's only one call to
poll() with a -1 timeout value. What I fail to understand is why I see
this null event in pcm_native.c, and nothing reported in userspace by
the wait_for_poll() loop in alsa-lib/test/pcm.c