From a38e1f4ed997bea3cbfbf8094a52c23570d59d2a Mon Sep 17 00:00:00 2001
From: Dongwon Kang <dwkang@google.com>
Date: Tue, 16 Jun 2015 15:28:17 -0700
Subject: [PATCH] Make MediaSessionService not blocked by AudioService.

Backgroud: As noted in b/20823981, MediaSessionService calls some
audio service methods while holding a lock and the audio service
methods also talk to other system services. And, deadlock happens when
the other system service fires another request to MediaSessionService
while holding its lock.

Example1) --- resolved by the change in MediaSessionRecord.java
T1: MediaSessionService.dispatchAdjustVolumeLocked()
     -> MediaSessionRecord.adjustVolume()
       -> +++AudioServiceInternal.adjustSuggestedStreamVolumeForUid()+++
         -> AudioService.adjustSuggestedStreamVolume()
           -> telecom.TelecomManager.isInCall() --- blocked by lock in TelecomManager.
T2: telecom.ConnectionServiceWrapper.handleCreateConnectionComplete()
     -> MediaSession.setActive()
       -> MediaSessionRecord$SessionStub.setActive()
         -> MediaSessionService.updateSession() --- blocked by lock in MediaSessionService.

Example2) --- resolved by the change in IAudioService.aidl
T1: MediaSessionService.dispatchAdjustVolumeLocked()
     -> IAudioService.adjustSuggestedStreamVolume()
       -> AudioService.adjustSuggestedStreamVolume()
         -> telecom.TelecomManager.isInCall() --- blocked by lock in TelecomManager.
T2: telecom.ConnectionServiceWrapper.handleCreateConnectionComplete()
     -> MediaSession.setActive()
       -> MediaSessionRecord$SessionStub.setActive()
         -> MediaSessionService.updateSession() --- blocked by lock in MediaSessionService.

Here, this change prevents the deadlock by making related audio IPC oneway
and calling the internal audio method without holding the lock.

Bug: 20823981
Change-Id: I4c4b2fc796f23d83be67f7edaacd7496c145d985
---
 media/java/android/media/IAudioService.aidl   |  2 +-
 .../server/media/MediaSessionRecord.java      | 34 +++++++++++++++----
 2 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/media/java/android/media/IAudioService.aidl b/media/java/android/media/IAudioService.aidl
index 8e9621875f30d..c75c7e5ef9b8a 100644
--- a/media/java/android/media/IAudioService.aidl
+++ b/media/java/android/media/IAudioService.aidl
@@ -40,7 +40,7 @@ import android.view.KeyEvent;
  */
 interface IAudioService {
 
-    void adjustSuggestedStreamVolume(int direction, int suggestedStreamType, int flags,
+    oneway void adjustSuggestedStreamVolume(int direction, int suggestedStreamType, int flags,
             String callingPackage, String caller);
 
     void adjustStreamVolume(int streamType, int direction, int flags, String callingPackage);
diff --git a/services/core/java/com/android/server/media/MediaSessionRecord.java b/services/core/java/com/android/server/media/MediaSessionRecord.java
index dca762c9f07f0..569a0fcf72042 100644
--- a/services/core/java/com/android/server/media/MediaSessionRecord.java
+++ b/services/core/java/com/android/server/media/MediaSessionRecord.java
@@ -242,19 +242,17 @@ public class MediaSessionRecord implements IBinder.DeathRecipient {
         }
         if (mVolumeType == PlaybackInfo.PLAYBACK_TYPE_LOCAL) {
             int stream = AudioAttributes.toLegacyStreamType(mAudioAttrs);
+            // Adjust the volume with a handler not to be blocked by other system service.
             if (useSuggested) {
                 if (AudioSystem.isStreamActive(stream, 0)) {
-                    mAudioManagerInternal.adjustSuggestedStreamVolumeForUid(stream, direction,
-                            flags, packageName, uid);
+                    postAdjustSuggestedStreamVolume(stream, direction, flags, packageName, uid);
                 } else {
                     flags |= previousFlagPlaySound;
-                    mAudioManagerInternal.adjustSuggestedStreamVolumeForUid(
-                            AudioManager.USE_DEFAULT_STREAM_TYPE, direction, flags, packageName,
-                            uid);
+                    postAdjustSuggestedStreamVolume(AudioManager.USE_DEFAULT_STREAM_TYPE, direction,
+                            flags, packageName, uid);
                 }
             } else {
-                mAudioManagerInternal.adjustStreamVolumeForUid(stream, direction, flags,
-                        packageName, uid);
+                postAdjustStreamVolume(stream, direction, flags, packageName, uid);
             }
         } else {
             if (mVolumeControlType == VolumeProvider.VOLUME_CONTROL_FIXED) {
@@ -461,6 +459,28 @@ public class MediaSessionRecord implements IBinder.DeathRecipient {
         return mPackageName + "/" + mTag;
     }
 
+    private void postAdjustSuggestedStreamVolume(final int streamType, final int direction,
+            final int flags, final String callingPackage, final int uid) {
+        mHandler.post(new Runnable() {
+            @Override
+            public void run() {
+                mAudioManagerInternal.adjustSuggestedStreamVolumeForUid(streamType, direction,
+                        flags, callingPackage, uid);
+            }
+        });
+    }
+
+    private void postAdjustStreamVolume(final int streamType, final int direction, final int flags,
+            final String callingPackage, final int uid) {
+        mHandler.post(new Runnable() {
+            @Override
+            public void run() {
+                mAudioManagerInternal.adjustStreamVolumeForUid(streamType, direction, flags,
+                        callingPackage, uid);
+            }
+        });
+    }
+
     private String getShortMetadataString() {
         int fields = mMetadata == null ? 0 : mMetadata.size();
         MediaDescription description = mMetadata == null ? null : mMetadata