[11u] RFR 8255269: Unsigned overflow in g1Policy.cpp

[Kemper, William]

Here's a patch based on jdk13u using the Skara CLI tools:

git hg-export 7e95c0a5
# HG changeset patch
# User phh
# Date 1603811625 0
#      Tue Oct 15:13:45 2020 +0000
8255269: Unsigned overflow in g1Policy.cpp
Reviewed-by: yan
Contributed-by: William Kemper <kemperw at amazon.com<mailto:kemperw at amazon.com>>

diff --git a/src/hotspot/share/gc/g1/g1Policy.cpp b/src/hotspot/share/gc/g1/g1Policy.cpp
index 91eceb7375..dec7f57de6 100644
--- a/src/hotspot/share/gc/g1/g1Policy.cpp
+++ b/src/hotspot/share/gc/g1/g1Policy.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2020, 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
@@ -692,11 +692,11 @@ void G1Policy::record_collection_pause_end(double pause_time_ms, size_t cards_sc
     _analytics->report_rs_length_diff((double) rs_length_diff);

     size_t freed_bytes = heap_used_bytes_before_gc - cur_used_bytes;
-    size_t copied_bytes = _collection_set->bytes_used_before() - freed_bytes;
-    double cost_per_byte_ms = 0.0;

-    if (copied_bytes > 0) {
-      cost_per_byte_ms = (average_time_ms(G1GCPhaseTimes::ObjCopy) + average_time_ms(G1GCPhaseTimes::OptObjCopy)) / (double) copied_bytes;
+    if (_collection_set->bytes_used_before() > freed_bytes) {
+      size_t copied_bytes = _collection_set->bytes_used_before() - freed_bytes;
+      double average_copy_time = average_time_ms(G1GCPhaseTimes::ObjCopy);
+      double cost_per_byte_ms = average_copy_time / (double) copied_bytes;
       _analytics->report_cost_per_byte_ms(cost_per_byte_ms, collector_state()->mark_or_rebuild_in_progress());
     }

I ran the jtreg tests for G1 against the release build on my workstation (x86, Ubuntu 18.04). The results were the same before and after the patch was applied:

test/hotspot/jtreg/gc/g1
Test results: passed: 56; failed: 4; error: 1

It doesn't look like the failures and error have anything to do with this change.

Thanks,
William