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Commit 7f1e3f3e authored by riddle_hsu's avatar riddle_hsu
Browse files

[ActivityManager] Prevent potential deadlock from system error dialog and InputMethodManager. 

Sympton:
When application crash in a special timing and system server's InputMethodManager is binding, deadlock may occur.

Root Cause:
Thread(1): When using InputMethodManager in system server, it will lock mH(handler) of InputMethodManager,
and sometimes it will call to InputMethodManagerService::showCurrentInputLocked and will call bindService at some condition,
then it will also lock ActivityManagerService.
Thread(2): When an application crashed, it will lock ActivityManager when showing crash dialog, inside the dialog,
it will call setEnabled of Button and lock mH of InputMethodManager.setEnable of TextView will lock IMM's handler.
So the deadlock happened as the flow: (2) lock AMS -> (1)lock mH -> (2)wait mH -> (1) wait AMS

Solution:
Reduce nested lock of error dialog: post message to let (2) lock mH after release AMS lock.

Change-Id: Id85c29406236db3b5fca9655fde1fcaf0afd1337
parent ef2e7667

services/java/com/android/server/am/BaseErrorDialog.java

100644 → 100755
+10 −5
Original line number Diff line number Diff line
@@ -27,6 +27,11 @@ import android.view.WindowManager; 
import android.widget.Button;



class BaseErrorDialog extends AlertDialog {

    private static final int ENABLE_BUTTONS = 0;

    private static final int DISABLE_BUTTONS = 1;



    private boolean mConsuming = true;



    public BaseErrorDialog(Context context) {

        super(context, com.android.internal.R.style.Theme_Dialog_AppError);
@@ -41,8 +46,8 @@ class BaseErrorDialog extends AlertDialog { 


    public void onStart() {

        super.onStart();

        setEnabled(false);

        mHandler.sendMessageDelayed(mHandler.obtainMessage(0), 1000);

        mHandler.sendEmptyMessage(DISABLE_BUTTONS);

        mHandler.sendMessageDelayed(mHandler.obtainMessage(ENABLE_BUTTONS), 1000);

    }



    public boolean dispatchKeyEvent(KeyEvent event) {
@@ -71,12 +76,12 @@ class BaseErrorDialog extends AlertDialog { 


    private Handler mHandler = new Handler() {

        public void handleMessage(Message msg) {

            if (msg.what == 0) {

            if (msg.what == ENABLE_BUTTONS) {

                mConsuming = false;

                setEnabled(true);

            } else if (msg.what == DISABLE_BUTTONS) {

                setEnabled(false);

            }

        }

    };



    private boolean mConsuming = true;

}