audioflinger: refresh fast track underrun state upon start

False underrun is detected when starting recycled fast tracks, which
leads to continuous fatal assertion failures and even AP reboot.

Track's last mObservedUnderruns isn't updated one at previous stop()
call. Hence, when we start the same track again, we should synchronize
it to the latest state instead of relying on stale one.

authored-by: Weiyin Jiang<wjiang@codeaurora.org>
CRs-Fixed: 803389
Bug: 19635137
Signed-off-by: Andy Hung <hunga@google.com>
Change-Id: Ia003a49c6896dba965798c062c98b8c367ef8369

1 files changed, 6 insertions, 2 deletions

diff --git a/services/audioflinger/Tracks.cpp b/services/audioflinger/Tracks.cpp
index 8329be4..38667b9 100644
--- a/services/audioflinger/Tracks.cpp
+++ b/services/audioflinger/Tracks.cpp
@@ -444,8 +444,6 @@ AudioFlinger::PlaybackThread::Track::Track(
         //       this means we are potentially denying other more important fast tracks from
         //       being created.  It would be better to allocate the index dynamically.
         mFastIndex = i;
-        // Read the initial underruns because this field is never cleared by the fast mixer
-        mObservedUnderruns = thread->getFastTrackUnderruns(i);
         thread->mFastTrackAvailMask &= ~(1 << i);
     }
 }
@@ -694,6 +692,12 @@ status_t AudioFlinger::PlaybackThread::Track::start(AudioSystem::sync_event_t ev
         }
 
         PlaybackThread *playbackThread = (PlaybackThread *)thread.get();
+        if (isFastTrack()) {
+            // refresh fast track underruns on start because that field is never cleared
+            // by the fast mixer; furthermore, the same track can be recycled, i.e. start
+            // after stop.
+            mObservedUnderruns = playbackThread->getFastTrackUnderruns(mFastIndex);
+        }
         status = playbackThread->addTrack_l(this);
         if (status == INVALID_OPERATION || status == PERMISSION_DENIED) {
             triggerEvents(AudioSystem::SYNC_EVENT_PRESENTATION_COMPLETE);