diff --git a/core/java/android/content/pm/PackageManager.java b/core/java/android/content/pm/PackageManager.java
index 98d64aa40ab17..be510c72e0bc0 100644
--- a/core/java/android/content/pm/PackageManager.java
+++ b/core/java/android/content/pm/PackageManager.java
@@ -983,7 +983,8 @@ public abstract class PackageManager {
      * Flag parameter for
      * {@link #setComponentEnabledSetting(android.content.ComponentName, int, int)} to indicate
      * that the given user's package restrictions state will be serialised to disk after the
-     * component state has been updated.
+     * component state has been updated. Note that this is synchronous disk access, so calls using
+     * this flag should be run on a background thread.
      */
     public static final int SYNCHRONOUS = 0x00000002;
 
diff --git a/services/core/java/android/content/pm/PackageManagerInternal.java b/services/core/java/android/content/pm/PackageManagerInternal.java
index 8b2bfa10a0299..1230bd79ff976 100644
--- a/services/core/java/android/content/pm/PackageManagerInternal.java
+++ b/services/core/java/android/content/pm/PackageManagerInternal.java
@@ -21,6 +21,7 @@ import android.annotation.IntDef;
 import android.annotation.NonNull;
 import android.annotation.Nullable;
 import android.annotation.UserIdInt;
+import android.annotation.WorkerThread;
 import android.content.ComponentName;
 import android.content.ContentResolver;
 import android.content.Intent;
@@ -261,6 +262,7 @@ public abstract class PackageManagerInternal {
     /**
      * Flushes package restrictions for the given user immediately to disk.
      */
+    @WorkerThread
     public abstract void flushPackageRestrictions(int userId);
 
     /**
diff --git a/services/core/java/com/android/server/pm/PackageManagerService.java b/services/core/java/com/android/server/pm/PackageManagerService.java
index 8bffeafb9efd9..077fc6f014295 100644
--- a/services/core/java/com/android/server/pm/PackageManagerService.java
+++ b/services/core/java/com/android/server/pm/PackageManagerService.java
@@ -130,6 +130,7 @@ import android.annotation.IntDef;
 import android.annotation.NonNull;
 import android.annotation.Nullable;
 import android.annotation.UserIdInt;
+import android.annotation.WorkerThread;
 import android.app.ActivityManager;
 import android.app.AppOpsManager;
 import android.app.ApplicationPackageManager;
@@ -213,7 +214,6 @@ import android.content.pm.dex.ArtManager;
 import android.content.pm.dex.DexMetadataHelper;
 import android.content.pm.dex.IArtManager;
 import android.content.pm.parsing.PackageInfoWithoutStateUtils;
-import android.content.pm.parsing.ParsingPackageRead;
 import android.content.pm.parsing.ParsingPackageUtils;
 import android.content.pm.parsing.component.ParsedActivity;
 import android.content.pm.parsing.component.ParsedInstrumentation;
@@ -20180,6 +20180,7 @@ public class PackageManagerService extends IPackageManager.Stub
         }
     }
 
+    @WorkerThread
     @Override
     public void flushPackageRestrictionsAsUser(int userId) {
         if (getInstantAppPackageName(Binder.getCallingUid()) != null) {
@@ -20197,6 +20198,8 @@ public class PackageManagerService extends IPackageManager.Stub
 
     @GuardedBy("mLock")
     private void flushPackageRestrictionsAsUserInternalLocked(int userId) {
+        // NOTE: this invokes synchronous disk access, so callers using this
+        // method should consider running on a background thread
         mSettings.writePackageRestrictionsLPr(userId);
         mDirtyUsers.remove(userId);
         if (mDirtyUsers.isEmpty()) {