8265682: G1: Mutex::_name dangling in HeapRegionRemSet references after JDK-8264146

Reviewed-by: dholmes, sjohanss

src/hotspot/share/runtime/mutex.cpp

@@ -258,6 +258,7 @@ bool Monitor::wait(int64_t timeout) {
 
 Mutex::~Mutex() {
   assert_owner(NULL);
+  os::free(const_cast<char*>(_name));
 }
 
 // Only Threads_lock and Heap_lock may be safepoint_check_sometimes.
@@ -266,9 +267,10 @@ bool is_sometimes_ok(const char* name) {
 }
 
 Mutex::Mutex(int Rank, const char * name, bool allow_vm_block,
-             SafepointCheckRequired safepoint_check_required) : _owner(NULL), _name(name) {
+             SafepointCheckRequired safepoint_check_required) : _owner(NULL) {
   assert(os::mutex_init_done(), "Too early!");
   assert(name != NULL, "Mutex requires a name");
+  _name = os::strdup(name, mtInternal);
 #ifdef ASSERT
   _allow_vm_block  = allow_vm_block;
   _rank            = Rank;

test/hotspot/gtest/runtime/test_mutex.cpp

@@ -25,8 +25,32 @@
 #include "runtime/interfaceSupport.inline.hpp"
 #include "runtime/mutex.hpp"
 #include "runtime/mutexLocker.hpp"
+#include "runtime/thread.hpp"
+#include "utilities/formatBuffer.hpp"
+#include "threadHelper.inline.hpp"
 #include "unittest.hpp"
 
+const int iterations = 10;
+static Mutex* m[iterations];
+static int i = 0;
+
+static void create_mutex(Thread* thr) {
+  m[i] = new Mutex(Mutex::leaf, FormatBuffer<128>("MyLock lock #%u", i), true, Mutex::_safepoint_check_never);
+  i++;
+}
+
+TEST_VM(MutexName, mutex_name) {
+  // Create mutexes in threads, where the names are created on the thread
+  // stacks and then check that their names are correct.
+  for (int i = 0; i < iterations; i++) {
+    nomt_test_doer(create_mutex);
+  }
+  for (int i = 0; i < iterations; i++) {
+    FormatBuffer<128> f("MyLock lock #%u", i);
+    ASSERT_STREQ(m[i]->name(), f.buffer()) << "Wrong name!";
+  }
+}
+
 #ifdef ASSERT
 
 const int rankA = 50;