On Tue, 9 Oct 2007, Dave Dillow wrote:
On Tue, 2007-10-09 at 11:48 +0200, Takashi Iwai wrote:
You need to unlock sis->hw_lock before calling snd_pcm_period_elapsed(). It may call snd_pcm_stop() at XRUN, and this invokes the trigger callback, which locks hw_lock again. Simply re-acquire hw_lock after calling snd_pcm_period_elapsed().
If I'm guaranteed that I'll never have my prepare() method called concurrently for the same substream, I think I can do away with the hw_lock completely -- though I need to think through scenarios about closing the stream and a late interrupt...
It looks like my prepare() gets called by snd_pcm_action_nonatomic() in sound/core/pcm_native.c, and that takes a read lock on the link semaphore, so the group won't be changed, but I don't see anything that would prevent prepare() being called twice on the same substream concurrently. So, I'll probably need to keep some locking to avoid an issue there, unless I'm missing a lock upstream.
You're right about that, prepare() can be called concurrently on the same substream, as can all the non-atomic functions like hw_params(). To be sure, I wrote a multi-threaded test program to execute concurrent ioctls.
There is a per-device mutex for open/close, so they can't run concurrently.
Note that the ALSA code does *not* handle concurrent calls to hw_params() or prepare() correctly. Your driver may have a lock, but the alsa core doesn't, and will read and write to the runtime parameters concurrently. See http://article.gmane.org/gmane.linux.alsa.devel/48846