openjdk-1.8.0/8166862-CMS-needs-klass_or_null_acquire.patch

# HG changeset patch
# User kbarrett
# Date 1477103211 14400
#      Fri Oct 21 22:26:51 2016 -0400
# Node ID 053ad011aea25994e337f1c5dc9bd4dcc63f38cb
# Parent  7f7c1e1fbc8a70f9730339872ddf56fee812304c
8166862: CMS needs klass_or_null_acquire
Summary: Change CMS non-assert uses of klass_or_null to klass_or_null_acquire.
Reviewed-by: tschatzl, mgerdin

diff --git a/src/share/vm/gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.cpp b/src/share/vm/gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.cpp
--- a/hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.cpp
+++ b/hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.cpp
@@ -998,18 +998,13 @@
       // and the klass read.
       OrderAccess::loadload();
 
-      // must read from what 'p' points to in each loop.
-      Klass* k = ((volatile oopDesc*)p)->klass_or_null();
+      // Ensure klass read before size.
+      Klass* k = oop(p)->klass_or_null_acquire();
       if (k != NULL) {
         assert(k->is_klass(), "Should really be klass oop.");
         oop o = (oop)p;
         assert(o->is_oop(true /* ignore mark word */), "Should be an oop.");
 
-        // Bugfix for systems with weak memory model (PPC64/IA64).
-        // The object o may be an array. Acquire to make sure that the array
-        // size (third word) is consistent.
-        OrderAccess::acquire();
-
         size_t res = o->size_given_klass(k);
         res = adjustObjectSize(res);
         assert(res != 0, "Block size should not be 0");
@@ -1057,21 +1052,13 @@
       // 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.
+      // Ensure klass read before size.
+      Klass* k = oop(p)->klass_or_null_acquire();
       if (k != NULL) {
         assert(k->is_klass(), "Should really be klass oop.");
         oop o = (oop)p;
         assert(o->is_oop(), "Should be an oop");
 
-        // Bugfix for systems with weak memory model (PPC64/IA64).
-        // The object o may be an array. Acquire to make sure that the array
-        // size (third word) is consistent.
-        OrderAccess::acquire();
-
         size_t res = o->size_given_klass(k);
         res = adjustObjectSize(res);
         assert(res != 0, "Block size should not be 0");
@@ -1124,7 +1111,7 @@
   // and the klass read.
   OrderAccess::loadload();
 
-  Klass* k = oop(p)->klass_or_null();
+  Klass* k = oop(p)->klass_or_null_acquire();
   if (k != NULL) {
     // Ignore mark word because it may have been used to
     // chain together promoted objects (the last one
diff --git a/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp b/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp
--- a/hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp
+++ b/hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp
@@ -6728,7 +6728,7 @@
 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
   size_t sz = 0;
   oop p = (oop)addr;
-  if (p->klass_or_null() != NULL) {
+  if (p->klass_or_null_acquire() != NULL) {
     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
   } else {
     sz = block_size_using_printezis_bits(addr);
@@ -7186,7 +7186,7 @@
   }
   if (_bitMap->isMarked(addr)) {
     // it's marked; is it potentially uninitialized?
-    if (p->klass_or_null() != NULL) {
+    if (p->klass_or_null_acquire() != NULL) {
         // an initialized object; ignore mark word in verification below
         // since we are running concurrent with mutators
         assert(p->is_oop(true), "should be an oop");
@@ -7227,7 +7227,7 @@
     }
   } else {
     // Either a not yet marked object or an uninitialized object
-    if (p->klass_or_null() == NULL) {
+    if (p->klass_or_null_acquire() == NULL) {
       // An uninitialized object, skip to the next card, since
       // we may not be able to read its P-bits yet.
       assert(size == 0, "Initial value");
@@ -7438,7 +7438,7 @@
     assert(_skipBits == 0, "tautology");
     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
     oop p = oop(addr);
-    if (p->klass_or_null() == NULL) {
+    if (p->klass_or_null_acquire() == NULL) {
       DEBUG_ONLY(if (!_verifying) {)
         // We re-dirty the cards on which this object lies and increase
         // the _threshold so that we'll come back to scan this object
@@ -7458,7 +7458,7 @@
           if (_threshold < end_card_addr) {
             _threshold = end_card_addr;
           }
-          if (p->klass_or_null() != NULL) {
+          if (p->klass_or_null_acquire() != NULL) {
             // Redirty the range of cards...
             _mut->mark_range(redirty_range);
           } // ...else the setting of klass will dirty the card anyway.
@@ -7609,7 +7609,7 @@
     assert(_skip_bits == 0, "tautology");
     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
     oop p = oop(addr);
-    if (p->klass_or_null() == NULL) {
+    if (p->klass_or_null_acquire() == NULL) {
       // in the case of Clean-on-Enter optimization, redirty card
       // and avoid clearing card by increasing  the threshold.
       return true;
@@ -8596,7 +8596,7 @@
            "alignment problem");
 
 #ifdef ASSERT
-      if (oop(addr)->klass_or_null() != NULL) {
+      if (oop(addr)->klass_or_null_acquire() != NULL) {
         // Ignore mark word because we are running concurrent with mutators
         assert(oop(addr)->is_oop(true), "live block should be an oop");
         assert(size ==
@@ -8607,7 +8607,7 @@
 
   } else {
     // This should be an initialized object that's alive.
-    assert(oop(addr)->klass_or_null() != NULL,
+    assert(oop(addr)->klass_or_null_acquire() != NULL,
            "Should be an initialized object");
     // Ignore mark word because we are running concurrent with mutators
     assert(oop(addr)->is_oop(true), "live block should be an oop");