From e11871e7de141a23d2d8297932664587790807cf Mon Sep 17 00:00:00 2001
From: Seigo Nonaka <nona@google.com>
Date: Wed, 19 Jul 2017 17:46:41 -0700
Subject: Fix race condition of removing surface.

mContainer.startingSurface can be replaced between posting
mRemoveStartingWindow and actually surface.remove() is called.

1. removeStartingWindow is called, then mRemoveStartingWindow is posted
   to mHandler
2. transferStartingWindow is called, then mContainer.startingWindow is
   replaced with new surface.
3. mHandler pops the callback and surface.remove() is called.

Here the remove is only called for replaced surface and never called for
older surface.

To fix this issue, surely removes the surface when the
removeStartingWindow is called.

Bug: 63156080
Bug: 63784898
Test: Watch /proc/<pid>/fd
Change-Id: Iccf13bdc98b4012168910305568f5dd4bbedbf54
Merged-In: I55e2c1b8fba32b3a19603e6ad4743f07576abd48
(cherry picked from commit 0bf3dc9822a4817b1fea1d819ab7abf61013ad8b)
---
 .../server/wm/AppWindowContainerController.java    | 73 +++++++++-------------
 1 file changed, 29 insertions(+), 44 deletions(-)

diff --git a/services/core/java/com/android/server/wm/AppWindowContainerController.java b/services/core/java/com/android/server/wm/AppWindowContainerController.java
index 4e4398ee9d91..741161b79187 100644
--- a/services/core/java/com/android/server/wm/AppWindowContainerController.java
+++ b/services/core/java/com/android/server/wm/AppWindowContainerController.java
@@ -115,41 +115,6 @@ public class AppWindowContainerController
         mListener.onWindowsGone();
     };
 
-    private final Runnable mRemoveStartingWindow = () -> {
-        StartingSurface surface = null;
-        synchronized (mWindowMap) {
-            if (mContainer == null) {
-                if (DEBUG_STARTING_WINDOW) Slog.v(TAG_WM, "mContainer was null while trying to"
-                        + " remove starting window");
-                return;
-            }
-            if (DEBUG_STARTING_WINDOW) Slog.v(TAG_WM, "Remove starting " + mContainer
-                    + ": startingWindow=" + mContainer.startingWindow
-                    + " startingView=" + mContainer.startingSurface);
-            if (mContainer.startingData != null) {
-                surface = mContainer.startingSurface;
-                mContainer.startingData = null;
-                mContainer.startingSurface = null;
-                mContainer.startingWindow = null;
-                mContainer.startingDisplayed = false;
-                if (surface == null && DEBUG_STARTING_WINDOW) {
-                    Slog.v(TAG_WM, "startingWindow was set but startingSurface==null, couldn't "
-                            + "remove");
-                }
-            } else if (DEBUG_STARTING_WINDOW) {
-                Slog.v(TAG_WM, "Tried to remove starting window but startingWindow was null:"
-                        + mContainer);
-            }
-        }
-        if (surface != null) {
-            try {
-                surface.remove();
-            } catch (Exception e) {
-                Slog.w(TAG_WM, "Exception when removing starting window", e);
-            }
-        }
-    };
-
     private final Runnable mAddStartingWindow = () -> {
         final StartingData startingData;
         final AppWindowToken container;
@@ -649,13 +614,6 @@ public class AppWindowContainerController
 
     public void removeStartingWindow() {
         synchronized (mWindowMap) {
-            if (mHandler.hasCallbacks(mRemoveStartingWindow)) {
-                // Already scheduled.
-                if (DEBUG_STARTING_WINDOW) Slog.v(TAG_WM, "Trying to remove starting window but "
-                        + "already scheduled");
-                return;
-            }
-
             if (mContainer.startingWindow == null) {
                 if (mContainer.startingData != null) {
                     // Starting window has not been added yet, but it is scheduled to be added.
@@ -667,9 +625,36 @@ public class AppWindowContainerController
                 return;
             }
 
+            final StartingSurface surface;
+            if (mContainer.startingData != null) {
+                surface = mContainer.startingSurface;
+                mContainer.startingData = null;
+                mContainer.startingSurface = null;
+                mContainer.startingWindow = null;
+                mContainer.startingDisplayed = false;
+                if (surface == null && DEBUG_STARTING_WINDOW) {
+                    Slog.v(TAG_WM, "startingWindow was set but startingSurface==null, couldn't "
+                            + "remove");
+                }
+            } else {
+                if (DEBUG_STARTING_WINDOW) {
+                    Slog.v(TAG_WM, "Tried to remove starting window but startingWindow was null:"
+                            + mContainer);
+                }
+                return;
+            }
+
             if (DEBUG_STARTING_WINDOW) Slog.v(TAG_WM, "Schedule remove starting " + mContainer
-                    + " startingWindow=" + mContainer.startingWindow);
-            mHandler.post(mRemoveStartingWindow);
+                    + " startingWindow=" + mContainer.startingWindow
+                    + " startingView=" + mContainer.startingSurface);
+            mHandler.post(() -> {
+                if (DEBUG_STARTING_WINDOW) Slog.v(TAG_WM, "Removing startingView=" + surface);
+                try {
+                    surface.remove();
+                } catch (Exception e) {
+                    Slog.w(TAG_WM, "Exception when removing starting window", e);
+                }
+            });
         }
     }
 
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