Commit 6e11e049 authored Oct 13, 2021 by jorgegil@google.com

Dump DisplayModeDirector state without locking mSyncRoot

The current locking order of DisplayManagerGlobal.mLock,
DisplayManagerService.mSyncRoot and SensorObserver.mSensorObserverLock
may cause a deadlock when an EVENT_DISPLAY_CHANGED event is handled
by MediaRouter.Static and DMD.SensorObserver at the same time as
a DisplayManagerService dump is in progress.

The locking order of onDisplayChanged is:
   - mSensorObserverLock -> DMG.mLock -> DMS.mSyncRoot
The locking order of DMS.dumpInternal is:
   - DMS.mSyncRoot -> mSensorOberverLock

This change removes the mSyncRoot locking during the DMD dump to keep
the lock ordering from going in a cycle. DMD already guards its state
during a dump with its own class lock, so holding mSyncRoot is not
really necessary.

Bug: 202515175
Test: builds
Change-Id: I464e570e7107b49633e599b25ef1d208c9fc76aa

parent f23eb51d

services/core/java/com/android/server/display/DisplayManagerService.java

+2 −3

Original line number	Diff line number	Diff line
		@@ -2062,9 +2062,6 @@ public final class DisplayManagerService extends SystemService {
		pw.println();
		mLogicalDisplayMapper.dumpLocked(pw);

		pw.println();
		mDisplayModeDirector.dump(pw);

		final int callbackCount = mCallbacks.size();
		pw.println();
		pw.println("Callbacks: size=" + callbackCount);
		@@ -2087,6 +2084,8 @@ public final class DisplayManagerService extends SystemService {
		pw.println();
		mPersistentDataStore.dump(pw);
		}
		pw.println();
		mDisplayModeDirector.dump(pw);
		}

		private static float[] getFloatArray(TypedArray array) {