8329528: G1 does not update TAMS correctly when dropping retained reg…

…ions during Concurrent Start pause

Reviewed-by: ayang, chegar

src/hotspot/share/gc/g1/g1YoungCollector.cpp

@@ -484,13 +484,8 @@ void G1YoungCollector::set_young_collection_default_active_worker_threads(){
 }
 
 void G1YoungCollector::pre_evacuate_collection_set(G1EvacInfo* evacuation_info) {
-
-  // Must be before collection set calculation, requires collection set to not
-  // be calculated yet.
-  if (collector_state()->in_concurrent_start_gc()) {
-    concurrent_mark()->pre_concurrent_start(_gc_cause);
-  }
-
+  // Flush various data in thread-local buffers to be able to determine the collection
+  // set
   {
     Ticks start = Ticks::now();
     G1PreEvacuateCollectionSetBatchTask cl;
@@ -501,6 +496,10 @@ void G1YoungCollector::pre_evacuate_collection_set(G1EvacInfo* evacuation_info)
   // Needs log buffers flushed.
   calculate_collection_set(evacuation_info, policy()->max_pause_time_ms());
 
+  if (collector_state()->in_concurrent_start_gc()) {
+    concurrent_mark()->pre_concurrent_start(_gc_cause);
+  }
+
   // Please see comment in g1CollectedHeap.hpp and
   // G1CollectedHeap::ref_processing_init() to see how
   // reference processing currently works in G1.

src/hotspot/share/gc/g1/g1YoungGCPreEvacuateTasks.hpp

@@ -29,6 +29,7 @@
 
 // Set of pre evacuate collection set tasks containing ("s" means serial):
 // - Retire TLAB and Flush Logs (Java threads)
+// - Flush pin count cache (Java threads)
 // - Flush Logs (s) (Non-Java threads)
 class G1PreEvacuateCollectionSetBatchTask : public G1BatchedTask {
   class JavaThreadRetireTLABAndFlushLogs;

src/hotspot/share/gc/g1/heapRegion.inline.hpp

@@ -289,7 +289,7 @@ inline void HeapRegion::reset_parsable_bottom() {
 
 inline void HeapRegion::note_start_of_marking() {
   assert(top_at_mark_start() == bottom(), "Region's TAMS must always be at bottom");
-  if (is_old_or_humongous() && !is_collection_set_candidate()) {
+  if (is_old_or_humongous() && !is_collection_set_candidate() && !in_collection_set()) {
     set_top_at_mark_start(top());
   }
 }

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

@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2024, 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 Check that TAMSes are correctly updated for regions dropped from
+ *          the retained collection set candidates during a Concurrent Start pause.
+ * @requires vm.gc.G1
+ * @requires vm.flagless
+ * @library /test/lib
+ * @build jdk.test.whitebox.WhiteBox
+ * @run driver jdk.test.lib.helpers.ClassFileInstaller jdk.test.whitebox.WhiteBox
+ * @run main/othervm -XX:+UseG1GC -XX:+UnlockDiagnosticVMOptions -XX:+UnlockExperimentalVMOptions
+                     -XX:+WhiteBoxAPI -Xbootclasspath/a:. -Xmx32m -XX:G1NumCollectionsKeepPinned=1
+                     -XX:+VerifyBeforeGC -XX:+VerifyAfterGC -XX:G1MixedGCLiveThresholdPercent=100
+                     -XX:G1HeapWastePercent=0 -Xlog:gc,gc+ergo+cset=trace gc.g1.pinnedobjs.TestDroppedRetainedTAMS
+ */
+
+package gc.g1.pinnedobjs;
+
+import jdk.test.whitebox.WhiteBox;
+
+public class TestDroppedRetainedTAMS {
+
+    private static final WhiteBox wb = WhiteBox.getWhiteBox();
+
+    private static final char[] dummy = new char[100];
+
+    public static void main(String[] args) {
+        wb.fullGC(); // Move the target dummy object to old gen.
+
+        wb.pinObject(dummy);
+
+        // After this concurrent cycle the pinned region will be in the the (marking)
+        // collection set candidates.
+        wb.g1RunConcurrentGC();
+
+        // Pass the Prepare mixed gc which will not do anything about the marking
+        // candidates.
+        wb.youngGC();
+        // Mixed GC. Will complete. That pinned region is now retained. The mixed gcs
+        // will end here.
+        wb.youngGC();
+
+        // The pinned region will be dropped from the retained candidates during the
+        // Concurrent Start GC, leaving that region's TAMS broken.
+        wb.g1RunConcurrentGC();
+
+        // Verification will find a lot of broken objects.
+        wb.youngGC();
+        System.out.println(dummy);
+    }
+}