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 _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
