From 4be998e634275b15fd40d7fd97772d20ec6ce445 Mon Sep 17 00:00:00 2001
From: simonis <unknown>
Date: Fri, 2 Dec 2016 11:07:27 +0100
Subject: [PATCH] 8170409: CMS: Crash in
 CardTableModRefBSForCTRS::process_chunk_boundaries Reviewed-by: simonis,
 tschatzl, mgerdin, dlong Contributed-by: gunter.haug@sap.com

---
 .../gc_implementation/parNew/parCardTableModRefBS.cpp | 11 ++++++++---
 src/share/vm/memory/cardTableModRefBS.hpp             |  2 +-
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/src/share/vm/gc_implementation/parNew/parCardTableModRefBS.cpp b/src/share/vm/gc_implementation/parNew/parCardTableModRefBS.cpp
index 9209f0d1a..34642187d 100644
--- a/src/share/vm/gc_implementation/parNew/parCardTableModRefBS.cpp
+++ b/src/share/vm/gc_implementation/parNew/parCardTableModRefBS.cpp
@@ -452,9 +452,13 @@ get_LNC_array_for_space(Space* sp,
   // event lock and do the read again in case some other thread had already
   // succeeded and done the resize.
   int cur_collection = Universe::heap()->total_collections();
-  if (_last_LNC_resizing_collection[i] != cur_collection) {
+  // Updated _last_LNC_resizing_collection[i] must not be visible before
+  // _lowest_non_clean and friends are visible. Therefore use acquire/release
+  // to guarantee this on non TSO architecures.
+  if (OrderAccess::load_acquire(&_last_LNC_resizing_collection[i]) != cur_collection) {
     MutexLocker x(ParGCRareEvent_lock);
-    if (_last_LNC_resizing_collection[i] != cur_collection) {
+    // This load_acquire is here for clarity only. The MutexLocker already fences.
+    if (OrderAccess::load_acquire(&_last_LNC_resizing_collection[i]) != cur_collection) {
       if (_lowest_non_clean[i] == NULL ||
           n_chunks != _lowest_non_clean_chunk_size[i]) {
 
@@ -474,7 +478,8 @@ get_LNC_array_for_space(Space* sp,
             _lowest_non_clean[i][j] = NULL;
         }
       }
-      _last_LNC_resizing_collection[i] = cur_collection;
+      // Make sure this gets visible only after _lowest_non_clean* was initialized
+      OrderAccess::release_store(&_last_LNC_resizing_collection[i], cur_collection);
     }
   }
   // In any case, now do the initialization.
diff --git a/src/share/vm/memory/cardTableModRefBS.hpp b/src/share/vm/memory/cardTableModRefBS.hpp
index c824e6185..ae15ba7ed 100644
--- a/src/share/vm/memory/cardTableModRefBS.hpp
+++ b/src/share/vm/memory/cardTableModRefBS.hpp
@@ -217,7 +217,7 @@ class CardTableModRefBS: public ModRefBarrierSet {
   CardArr* _lowest_non_clean;
   size_t*  _lowest_non_clean_chunk_size;
   uintptr_t* _lowest_non_clean_base_chunk_index;
-  int* _last_LNC_resizing_collection;
+  volatile int* _last_LNC_resizing_collection;
 
   // Initializes "lowest_non_clean" to point to the array for the region
   // covering "sp", and "lowest_non_clean_base_chunk_index" to the chunk
-- 
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