commit c4f28a419615a6035085e74fbd7670f27faf3d0f
author Shibin George <shibing@codeaurora.org> Tue Jun 28 15:56:50 2016 +0530
committer Shibin George <shibing@codeaurora.org> Wed Jul 06 05:00:43 2016 +0000
tree 551db306b0732faf3fed53d92590e89b01e12709
parent 326e55a3e25366b45e152ab5234b42dee781e8ac

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>

services/core/java/com/android/server/media/MediaSessionService.java

diff --git a/services/core/java/com/android/server/media/MediaSessionService.java b/services/core/java/com/android/server/media/MediaSessionService.java
index 1a320d2..b719063 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 @@
     }
 
     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 @@
                 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 @@
                         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 @@
                         } 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 "