src/share/vm/gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.cpp

rev 9232 : 8248851: CMS: Missing memory fences between free chunk check and klass read
Reviewed-by: aph, kbarrett, dholmes
Contributed-by: wangshuai94@huawei.com

*** 1,7 ****
  /*
!  * Copyright (c) 2001, 2014, 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.
--- 1,7 ----
  /*
!  * 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
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.
*** 992,1001 ****
--- 992,1005 ----
        if (FreeChunk::indicatesFreeChunk(p)) {
          assert(res != 0, "Block size should not be 0");
          return res;
        }
      } else {
+       // The barrier is required to prevent reordering of the free chunk check
+       // and the klass read.
+       OrderAccess::loadload();
+ 
        // must read from what 'p' points to in each loop.
        Klass* k = ((volatile oopDesc*)p)->klass_or_null();
        if (k != NULL) {
          assert(k->is_klass(), "Should really be klass oop.");
          oop o = (oop)p;
*** 1047,1056 ****
--- 1051,1064 ----
          assert(res != 0, "Block size should not be 0");
          assert(loops == 0, "Should be 0");
          return res;
        }
      } else {
+       // The barrier is required to prevent reordering of the free chunk check
+       // and the klass read.
+       OrderAccess::loadload();
+ 
        // must read from what 'p' points to in each loop.
        Klass* k = ((volatile oopDesc*)p)->klass_or_null();
        // We trust the size of any object that has a non-NULL
        // klass and (for those in the perm gen) is parsable
        // -- irrespective of its conc_safe-ty.
*** 1109,1118 ****
--- 1117,1131 ----
    // and those objects (if garbage) may have been modified to hold
    // live range information.
    // assert(CollectedHeap::use_parallel_gc_threads() || _bt.block_start(p) == p,
    //        "Should be a block boundary");
    if (FreeChunk::indicatesFreeChunk(p)) return false;
+ 
+   // The barrier is required to prevent reordering of the free chunk check
+   // and the klass read.
+   OrderAccess::loadload();
+ 
    Klass* k = oop(p)->klass_or_null();
    if (k != NULL) {
      // Ignore mark word because it may have been used to
      // chain together promoted objects (the last one
      // would have a null value).