8351921: G1: Pinned regions with pinned objects only reachable by native code crash VM

Reviewed-by: ayang, iwalulya

Author: Thomas Schatzl

test/hotspot/jtreg/gc/g1/pinnedobjs/TestPinnedEvacEmpty.java

@@ -0,0 +1,89 @@
+/*
+ * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/* @test
+ * @summary Test that pinned regions with no Java references into them
+ *          do not make the garbage collector reclaim that region.
+ *          This test simulates this behavior using Whitebox/Unsafe methods
+ *          to pin a Java object in a region with no other pinnable objects and
+*           lose the reference to it before the garbage collection.
+ * @requires vm.gc.G1
+ * @requires vm.debug
+ * @library /test/lib
+ * @modules java.base/jdk.internal.misc:+open
+ *          java.management
+ * @build jdk.test.whitebox.WhiteBox
+ * @run driver jdk.test.lib.helpers.ClassFileInstaller jdk.test.whitebox.WhiteBox
+ * @run main/othervm -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI -XX:+UseG1GC
+ *      -Xbootclasspath/a:. -Xlog:gc=debug,gc+ergo+cset=trace,gc+phases=debug -XX:G1HeapRegionSize=1m -Xms30m  gc.g1.pinnedobjs.TestPinnedEvacEmpty
+ */
+
+package gc.g1.pinnedobjs;
+
+import jdk.internal.misc.Unsafe;
+
+import jdk.test.lib.Asserts;
+import jdk.test.lib.process.OutputAnalyzer;
+import jdk.test.lib.process.ProcessTools;
+import jdk.test.whitebox.WhiteBox;
+
+public class TestPinnedEvacEmpty {
+
+    private static final jdk.internal.misc.Unsafe unsafe = Unsafe.getUnsafe();
+    private static final WhiteBox wb = WhiteBox.getWhiteBox();
+
+    private static final long objSize = wb.getObjectSize(new Object());
+
+    // How many j.l.Object should we allocate when creating garbage.
+    private static final long numAllocations = 1024 * 1024 * 3 / objSize;
+
+    public static void main(String[] args) throws Exception {
+        // Remove garbage from VM initialization.
+        wb.fullGC();
+
+        // Allocate garbage so that the target object will be in a new region.
+        for (int i = 0; i < numAllocations; i++) {
+          Object z = new Object();
+        }
+        int[] o = new int[100];  // The target object to pin.
+        // Further allocate garbage so that any additional allocations of potentially
+        // pinned objects can not be allocated in the same region as the target object.
+        for (int i = 0; i < numAllocations; i++) {
+          Object z = new Object();
+        }
+
+        Asserts.assertTrue(!wb.isObjectInOldGen(o), "should not be in old gen already");
+
+        // Pin the object.
+        wb.pinObject(o);
+
+        // And forget the (Java) reference to the int array. After this, the garbage
+        // collection should find a completely empty pinned region. The collector
+        // must not collect/free it.
+        o = null;
+
+        // Do garbage collection to zap the data in the pinned region.
+        wb.youngGC();
+    }
+}
+