From 895d981852219cd087605f6ac2b04beb876a863d Mon Sep 17 00:00:00 2001
From: Ashok Mutyala <quic_c_nmutya@quicinc.com>
Date: Wed, 11 Aug 2021 11:17:19 +0000
Subject: [PATCH] Avoid the scenario where Contexts list filled with null value
 in ShowAnrDialogs()

Problem: Framework Reboot i.e., NullPointer Exception in android.ui Thread
E AndroidRuntime: FATAL EXCEPTION IN SYSTEM PROCESS: android.ui
E AndroidRuntime: java.lang.NullPointerException: Attempt to invoke virtual method
'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference

E AndroidRuntime: **at android.app.Dialog.<init>(Dialog.java:199)
E AndroidRuntime: **at android.app.AlertDialog.<init>(AlertDialog.java:204)
E AndroidRuntime: **at android.app.AlertDialog.<init>(AlertDialog.java:200)
E AndroidRuntime: **at com.android.server.am.BaseErrorDialog.<init>(BaseErrorDialog.java:39)
E AndroidRuntime: **at com.android.server.am.AppNotRespondingDialog.<init>(AppNotRespondingDialog.java:53)
E AndroidRuntime: **at com.android.server.am.ErrorDialogController.showAnrDialogs(ErrorDialogController.java:183)
E AndroidRuntime: **at com.android.server.am.AppErrors.handleShowAnrUi(AppErrors.java:1077)

Analysis:
As Context Object is passed from showAnrDialogs method and will be retrieved from getDisplayContextWithErrorDialogs
And list of context objects will be filled by querying from RootWindowContainer.getDisplayUiContext and this method is
Annotated with Nullable. So, the possibility could be null value filled in the context object List.

Bug: 196189977
Test: Stability Test

Change-Id: Ib944fc5ffc8bcca999c75f99d462d441e555fcda
---
 .../java/com/android/server/wm/WindowProcessController.java     | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/services/core/java/com/android/server/wm/WindowProcessController.java b/services/core/java/com/android/server/wm/WindowProcessController.java
index e6a35f1267b55..1f8a437abe085 100644
--- a/services/core/java/com/android/server/wm/WindowProcessController.java
+++ b/services/core/java/com/android/server/wm/WindowProcessController.java
@@ -908,7 +908,7 @@ public class WindowProcessController extends ConfigurationContainer<Configuratio
                 final int displayId = r.getDisplayId();
                 final Context c = root.getDisplayUiContext(displayId);
 
-                if (r.mVisibleRequested && !displayContexts.contains(c)) {
+                if (c != null && r.mVisibleRequested && !displayContexts.contains(c)) {
                     displayContexts.add(c);
                 }
             }