Merge "Don't request sync again for reparented WC" into tm-dev am: 7b0ceb4ff1

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/18148567

Change-Id: Ifaf1d413128f01b9a83ba2651895c6aed668fa8a
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>

services/core/java/com/android/server/wm/WindowContainer.java

@@ -3749,8 +3749,16 @@ class WindowContainer<E extends WindowContainer> extends ConfigurationContainer<
             }
             // Otherwise this is the "root" of a synced subtree, so continue on to preparation.
         }
+
         // This container's situation has changed so we need to restart its sync.
-        mSyncState = SYNC_STATE_NONE;
+        // We cannot reset the sync without a chance of a deadlock since it will request a new
+        // buffer from the app process. This could cause issues if the app has run out of buffers
+        // since the previous buffer was already synced and is still held in a transaction.
+        // Resetting syncState violates the policies outlined in BlastSyncEngine.md so for now
+        // disable this when shell transitions is disabled.
+        if (mTransitionController.isShellTransitionsEnabled()) {
+            mSyncState = SYNC_STATE_NONE;
+        }
         prepareSync();
     }