Fix deadlock in MediaSessionService during getCurrentUser()

SystemServiceMAnager.stopUser() acquires ActivityManagerService
lock first and then acquires MediaSessionService.mLock during
onStopUser(). MediaSessionService.onSwitchUser(), on the other
hand, acquires mLock first and ActivityManagerService lock next.
This is a potential deadlock situation which can be resolved by
moving getCurrentUser() out of synchronized block. This will
release mLock sooner and avoid the deadlock.

https://code.google.com/p/android/issues/detail?id=214469

Change-Id: Ieb4520d60af6ca38496ca933da0cd9ae096a9408
Signed-off-by: Shibin George <shibing@codeaurora.org>

1 files changed, 4 insertions, 5 deletions

diff --git a/services/core/java/com/android/server/media/MediaSessionService.java b/services/core/java/com/android/server/media/MediaSessionService.java
index 1a320d2bdb80..b7190638b0e5 100644
--- a/services/core/java/com/android/server/media/MediaSessionService.java
+++ b/services/core/java/com/android/server/media/MediaSessionService.java
@@ -227,8 +227,8 @@ public class MediaSessionService extends SystemService implements Monitor {
     }
 
     private void updateUser() {
+        int userId = ActivityManager.getCurrentUser();
         synchronized (mLock) {
-            int userId = ActivityManager.getCurrentUser();
             if (mCurrentUserId != userId) {
                 final int oldUserId = mCurrentUserId;
                 mCurrentUserId = userId; // do this first
@@ -764,7 +764,7 @@ public class MediaSessionService extends SystemService implements Monitor {
                 synchronized (mLock) {
                     // If we don't have a media button receiver to fall back on
                     // include non-playing sessions for dispatching
-                    UserRecord ur = mUserRecords.get(ActivityManager.getCurrentUser());
+                    UserRecord ur = mUserRecords.get(mCurrentUserId);
                     boolean useNotPlayingSessions = (ur == null) ||
                             (ur.mLastMediaButtonReceiver == null
                                 && ur.mRestoredMediaButtonReceiver == null);
@@ -957,8 +957,7 @@ public class MediaSessionService extends SystemService implements Monitor {
                         mKeyEventReceiver);
             } else {
                 // Launch the last PendingIntent we had with priority
-                int userId = ActivityManager.getCurrentUser();
-                UserRecord user = mUserRecords.get(userId);
+                UserRecord user = mUserRecords.get(mCurrentUserId);
                 if (user.mLastMediaButtonReceiver != null
                         || user.mRestoredMediaButtonReceiver != null) {
                     if (DEBUG) {
@@ -979,7 +978,7 @@ public class MediaSessionService extends SystemService implements Monitor {
                         } else {
                             mediaButtonIntent.setComponent(user.mRestoredMediaButtonReceiver);
                             getContext().sendBroadcastAsUser(mediaButtonIntent,
-                                    new UserHandle(userId));
+                                    new UserHandle(mCurrentUserId));
                         }
                     } catch (CanceledException e) {
                         Log.i(TAG, "Error sending key event to media button receiver "