From e9ff4606449c075d464e667410392e23afab7a45 Mon Sep 17 00:00:00 2001
From: Jorim Jaggi <jjaggi@google.com>
Date: Wed, 14 Jun 2017 18:09:58 -0700
Subject: Actually do not hold WM lock while closing transaction

Test: go/wm-smoke
Test: Quick switch 100x, observe no delay
Change-Id: I46022a23f749c52ba7f46e105679d728277970bd
Fixes: 62444483
---
 .../core/java/com/android/server/wm/WindowAnimator.java  |  5 ++++-
 .../java/com/android/server/wm/WindowManagerService.java | 16 ++++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/services/core/java/com/android/server/wm/WindowAnimator.java b/services/core/java/com/android/server/wm/WindowAnimator.java
index 03b5b827db74..07c29c05095a 100644
--- a/services/core/java/com/android/server/wm/WindowAnimator.java
+++ b/services/core/java/com/android/server/wm/WindowAnimator.java
@@ -227,7 +227,10 @@ public class WindowAnimator {
             Slog.wtf(TAG, "Unhandled exception in Window Manager", e);
         } finally {
             if (transactionOpen) {
-                mService.closeSurfaceTransaction();
+
+                // Do not hold window manager lock while closing the transaction, as this might be
+                // blocking until the next frame, which can lead to total lock starvation.
+                mService.closeSurfaceTransaction(false /* withLockHeld */);
                 if (SHOW_TRANSACTIONS) Slog.i(TAG, "<<< CLOSE TRANSACTION animate");
             }
         }
diff --git a/services/core/java/com/android/server/wm/WindowManagerService.java b/services/core/java/com/android/server/wm/WindowManagerService.java
index 768b03a249b8..68818acb6a90 100644
--- a/services/core/java/com/android/server/wm/WindowManagerService.java
+++ b/services/core/java/com/android/server/wm/WindowManagerService.java
@@ -891,10 +891,26 @@ public class WindowManagerService extends IWindowManager.Stub
     }
 
     void closeSurfaceTransaction() {
+        closeSurfaceTransaction(true /* withLockHeld */);
+    }
+
+    /**
+     * Closes a surface transaction.
+     *
+     * @param withLockHeld Whether to acquire the window manager while doing so. In some cases
+     *                     holding the lock my lead to starvation in WM in case closeTransaction
+     *                     blocks and we call it repeatedly, like we do for animations.
+     */
+    void closeSurfaceTransaction(boolean withLockHeld) {
         synchronized (mWindowMap) {
             if (mRoot.mSurfaceTraceEnabled) {
                 mRoot.mRemoteEventTrace.closeSurfaceTransaction();
             }
+            if (withLockHeld) {
+                SurfaceControl.closeTransaction();
+            }
+        }
+        if (!withLockHeld) {
             SurfaceControl.closeTransaction();
         }
     }
-- 
cgit v1.2.3-59-g8ed1b