6952853: SIGSEGV with UseAdaptiveGCBoundary on 64b linux running jvm2008

Summary: Shrinking of a generation and the corresponding card table was causing part of the card table to be uncommitted.
Reviewed-by: jcoomes

src/share/vm/gc_implementation/parallelScavenge/cardTableExtension.cpp

 /*
- * Copyright (c) 2001, 2008, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2010, 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
@@ -566,14 +566,14 @@ void CardTableExtension::resize_covered_region_by_end(int changed_region,
 #endif
 
   // Commit new or uncommit old pages, if necessary.
-  resize_commit_uncommit(changed_region, new_region);
+  if (resize_commit_uncommit(changed_region, new_region)) {
+    // Set the new start of the committed region
+    resize_update_committed_table(changed_region, new_region);
+  }
 
   // Update card table entries
   resize_update_card_table_entries(changed_region, new_region);
 
-  // Set the new start of the committed region
-  resize_update_committed_table(changed_region, new_region);
-
   // Update the covered region
   resize_update_covered_table(changed_region, new_region);
 
@@ -604,8 +604,9 @@ void CardTableExtension::resize_covered_region_by_end(int changed_region,
   debug_only(verify_guard();)
 }
 
-void CardTableExtension::resize_commit_uncommit(int changed_region,
+bool CardTableExtension::resize_commit_uncommit(int changed_region,
                                                 MemRegion new_region) {
+  bool result = false;
   // Commit new or uncommit old pages, if necessary.
   MemRegion cur_committed = _committed[changed_region];
   assert(_covered[changed_region].end() == new_region.end(),
@@ -675,20 +676,31 @@ void CardTableExtension::resize_commit_uncommit(int changed_region,
                               "card table expansion");
       }
     }
+    result = true;
   } else if (new_start_aligned > cur_committed.start()) {
     // Shrink the committed region
+#if 0 // uncommitting space is currently unsafe because of the interactions
+      // of growing and shrinking regions.  One region A can uncommit space
+      // that it owns but which is being used by another region B (maybe).
+      // Region B has not committed the space because it was already
+      // committed by region A.
     MemRegion uncommit_region = committed_unique_to_self(changed_region,
       MemRegion(cur_committed.start(), new_start_aligned));
     if (!uncommit_region.is_empty()) {
       if (!os::uncommit_memory((char*)uncommit_region.start(),
                                uncommit_region.byte_size())) {
-        vm_exit_out_of_memory(uncommit_region.byte_size(),
-          "card table contraction");
+        // If the uncommit fails, ignore it.  Let the
+        // committed table resizing go even though the committed
+        // table will over state the committed space.
       }
     }
+#else
+    assert(!result, "Should be false with current workaround");
+#endif
   }
   assert(_committed[changed_region].end() == cur_committed.end(),
     "end should not change");
+  return result;
 }
 
 void CardTableExtension::resize_update_committed_table(int changed_region,

src/share/vm/gc_implementation/parallelScavenge/cardTableExtension.hpp

 /*
- * Copyright (c) 2001, 2008, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2010, 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
@@ -30,7 +30,9 @@ class GCTaskQueue;
 class CardTableExtension : public CardTableModRefBS {
  private:
   // Support methods for resizing the card table.
-  void resize_commit_uncommit(int changed_region, MemRegion new_region);
+  // resize_commit_uncommit() returns true if the pages were committed or
+  // uncommitted
+  bool resize_commit_uncommit(int changed_region, MemRegion new_region);
   void resize_update_card_table_entries(int changed_region,
                                         MemRegion new_region);
   void resize_update_committed_table(int changed_region, MemRegion new_region);

src/share/vm/memory/cardTableModRefBS.cpp

 /*
- * Copyright (c) 2000, 2009, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 2010, 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
@@ -284,12 +284,19 @@ void CardTableModRefBS::resize_covered_region(MemRegion new_region) {
         committed_unique_to_self(ind, MemRegion(new_end_aligned,
                                                 cur_committed.end()));
       if (!uncommit_region.is_empty()) {
-        if (!os::uncommit_memory((char*)uncommit_region.start(),
-                                 uncommit_region.byte_size())) {
-          assert(false, "Card table contraction failed");
-          // The call failed so don't change the end of the
-          // committed region.  This is better than taking the
-          // VM down.
+        // It is not safe to uncommit cards if the boundary between
+        // the generations is moving.  A shrink can uncommit cards
+        // owned by generation A but being used by generation B.
+        if (!UseAdaptiveGCBoundary) {
+          if (!os::uncommit_memory((char*)uncommit_region.start(),
+                                   uncommit_region.byte_size())) {
+            assert(false, "Card table contraction failed");
+            // The call failed so don't change the end of the
+            // committed region.  This is better than taking the
+            // VM down.
+            new_end_aligned = _committed[ind].end();
+          }
+        } else {
           new_end_aligned = _committed[ind].end();
         }
       }
@@ -297,6 +304,19 @@ void CardTableModRefBS::resize_covered_region(MemRegion new_region) {
     // In any case, we can reset the end of the current committed entry.
     _committed[ind].set_end(new_end_aligned);
 
+#ifdef ASSERT
+    // Check that the last card in the new region is committed according
+    // to the tables.
+    bool covered = false;
+    for (int cr = 0; cr < _cur_covered_regions; cr++) {
+      if (_committed[cr].contains(new_end - 1)) {
+        covered = true;
+        break;
+      }
+    }
+    assert(covered, "Card for end of new region not committed");
+#endif
+
     // The default of 0 is not necessarily clean cards.
     jbyte* entry;
     if (old_region.last() < _whole_heap.start()) {
@@ -354,6 +374,9 @@ void CardTableModRefBS::resize_covered_region(MemRegion new_region) {
                   addr_for((jbyte*) _committed[ind].start()),
                   addr_for((jbyte*) _committed[ind].last()));
   }
+  // Touch the last card of the covered region to show that it
+  // is committed (or SEGV).
+  debug_only(*byte_for(_covered[ind].last());)
   debug_only(verify_guard();)
 }