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Commit d46f12bf authored by riddle_hsu's avatar riddle_hsu Committed by Steve Kondik
Browse files

Avoid deadlock between ActivityManagerService and ProcessStatsService. 

Root Cause:
Case 1
getStatsOverTime(#483) // lock mWriteLock, wait AMS
async performWriteState(#269) // lock mPendingWriteLock, wait mWriteLock
writeStateLocked(#218) // lock AMS, wait mPendingWriteLock

Case 2
getStatsOverTime(#483) // lock mWriteLock, wait AMS
writeStateSyncLocked,writeStateLocked(#269) // lock AMS, wait mWriteLock

Solution:
Reduce nested lock.

Others also post the same solution:
I437a5cedceb34292a6bd1d9e7610f52b1478e424

Change-Id: Ie9395f3f6359fe59e2282674fcfec9d123e53f25
parent b98529ea

services/core/java/com/android/server/am/ProcessStatsService.java

+16 −16
Original line number Diff line number Diff line
@@ -445,14 +445,14 @@ public final class ProcessStatsService extends IProcessStats.Stub { 
        mAm.mContext.enforceCallingOrSelfPermission(

                android.Manifest.permission.PACKAGE_USAGE_STATS, null);

        Parcel current = Parcel.obtain();

        mWriteLock.lock();

        try {

        synchronized (mAm) {

            long now = SystemClock.uptimeMillis();

            mProcessStats.mTimePeriodEndRealtime = SystemClock.elapsedRealtime();

            mProcessStats.mTimePeriodEndUptime = now;

            mProcessStats.writeToParcel(current, now, 0);

        }

        mWriteLock.lock();

        try {

            if (historic != null) {

                ArrayList<String> files = getCommittedFiles(0, false, true);

                if (files != null) {
@@ -476,8 +476,6 @@ public final class ProcessStatsService extends IProcessStats.Stub { 
    public ParcelFileDescriptor getStatsOverTime(long minTime) {

        mAm.mContext.enforceCallingOrSelfPermission(

                android.Manifest.permission.PACKAGE_USAGE_STATS, null);

        mWriteLock.lock();

        try {

        Parcel current = Parcel.obtain();

        long curTime;

        synchronized (mAm) {
@@ -488,6 +486,8 @@ public final class ProcessStatsService extends IProcessStats.Stub { 
            curTime = mProcessStats.mTimePeriodEndRealtime

                    - mProcessStats.mTimePeriodStartRealtime;

        }

        mWriteLock.lock();

        try {

            if (curTime < minTime) {

                // Need to add in older stats to reach desired time.

                ArrayList<String> files = getCommittedFiles(0, false, true);