--- a/hotspot/src/share/vm/runtime/mutex.cpp	Thu Jan 31 14:56:50 2008 -0500
+++ b/hotspot/src/share/vm/runtime/mutex.cpp	Tue Feb 05 23:21:57 2008 -0800
@@ -1119,10 +1119,15 @@
   assert ((UNS(_owner)|UNS(_LockWord.FullWord)|UNS(_EntryList)|UNS(_WaitSet)|UNS(_OnDeck)) == 0, "") ;
 }
 
-void Monitor::ClearMonitor (Monitor * m) {
+void Monitor::ClearMonitor (Monitor * m, const char *name) {
   m->_owner             = NULL ;
   m->_snuck             = false ;
-  m->_name              = "UNKNOWN" ;
+  if (name == NULL) {
+    strcpy(m->_name, "UNKNOWN") ;
+  } else {
+    strncpy(m->_name, name, MONITOR_NAME_LEN - 1);
+    m->_name[MONITOR_NAME_LEN - 1] = '\0';
+  }
   m->_LockWord.FullWord = 0 ;
   m->_EntryList         = NULL ;
   m->_OnDeck            = NULL ;
@@ -1133,7 +1138,7 @@
 Monitor::Monitor() { ClearMonitor(this); }
 
 Monitor::Monitor (int Rank, const char * name, bool allow_vm_block) {
-  ClearMonitor (this) ;
+  ClearMonitor (this, name) ;
 #ifdef ASSERT
   _allow_vm_block  = allow_vm_block;
   _rank            = Rank ;
@@ -1145,7 +1150,7 @@
 }
 
 Mutex::Mutex (int Rank, const char * name, bool allow_vm_block) {
-  ClearMonitor ((Monitor *) this) ;
+  ClearMonitor ((Monitor *) this, name) ;
 #ifdef ASSERT
  _allow_vm_block   = allow_vm_block;
  _rank             = Rank ;

--- a/hotspot/src/share/vm/runtime/mutex.hpp	Thu Jan 31 14:56:50 2008 -0500
+++ b/hotspot/src/share/vm/runtime/mutex.hpp	Tue Feb 05 23:21:57 2008 -0800
@@ -82,6 +82,9 @@
 // *in that order*.  If their implementations change such that these
 // assumptions are violated, a whole lot of code will break.
 
+// The default length of monitor name is choosen to be 64 to avoid false sharing.
+static const int MONITOR_NAME_LEN = 64;
+
 class Monitor : public CHeapObj {
 
  public:
@@ -126,9 +129,8 @@
   volatile intptr_t _WaitLock [1] ;      // Protects _WaitSet
   ParkEvent * volatile  _WaitSet ;       // LL of ParkEvents
   volatile bool     _snuck;              // Used for sneaky locking (evil).
-  const char * _name;                    // Name of mutex
   int NotifyCount ;                      // diagnostic assist
-  double pad [8] ;                       // avoid false sharing
+  char _name[MONITOR_NAME_LEN];          // Name of mutex
 
   // Debugging fields for naming, deadlock detection, etc. (some only used in debug mode)
 #ifndef PRODUCT
@@ -170,7 +172,7 @@
    int  ILocked () ;
 
  protected:
-   static void ClearMonitor (Monitor * m) ;
+   static void ClearMonitor (Monitor * m, const char* name = NULL) ;
    Monitor() ;
 
  public:

--- a/hotspot/src/share/vm/runtime/mutexLocker.cpp	Thu Jan 31 14:56:50 2008 -0500
+++ b/hotspot/src/share/vm/runtime/mutexLocker.cpp	Tue Feb 05 23:21:57 2008 -0800
@@ -188,10 +188,6 @@
 
   def(Safepoint_lock               , Monitor, safepoint,   true ); // locks SnippetCache_lock/Threads_lock
 
-  if (!UseMembar) {
-    def(SerializePage_lock         , Monitor, leaf,        true );
-  }
-
   def(Threads_lock                 , Monitor, barrier,     true );
 
   def(VMOperationQueue_lock        , Monitor, nonleaf,     true ); // VM_thread allowed to block on these

--- a/hotspot/src/share/vm/runtime/mutexLocker.hpp	Thu Jan 31 14:56:50 2008 -0500
+++ b/hotspot/src/share/vm/runtime/mutexLocker.hpp	Tue Feb 05 23:21:57 2008 -0800
@@ -52,7 +52,6 @@
 extern Monitor* VMOperationQueue_lock;           // a lock on queue of vm_operations waiting to execute
 extern Monitor* VMOperationRequest_lock;         // a lock on Threads waiting for a vm_operation to terminate
 extern Monitor* Safepoint_lock;                  // a lock used by the safepoint abstraction
-extern Monitor* SerializePage_lock;              // a lock used when VMThread changing serialize memory page permission during safepoint
 extern Monitor* Threads_lock;                    // a lock on the Threads table of active Java threads
                                                  // (also used by Safepoints too to block threads creation/destruction)
 extern Monitor* CGC_lock;                        // used for coordination between

--- a/hotspot/src/share/vm/runtime/os.cpp	Thu Jan 31 14:56:50 2008 -0500
+++ b/hotspot/src/share/vm/runtime/os.cpp	Tue Feb 05 23:21:57 2008 -0800
@@ -956,7 +956,6 @@
     return true;
 }
 
-
 void os::set_memory_serialize_page(address page) {
   int count = log2_intptr(sizeof(class JavaThread)) - log2_intptr(64);
   _mem_serialize_page = (volatile int32_t *)page;
@@ -967,6 +966,8 @@
   set_serialize_page_mask((uintptr_t)(vm_page_size() - sizeof(int32_t)));
 }
 
+static volatile intptr_t SerializePageLock = 0;
+
 // This method is called from signal handler when SIGSEGV occurs while the current
 // thread tries to store to the "read-only" memory serialize page during state
 // transition.
@@ -974,15 +975,14 @@
   if (TraceSafepoint) {
     tty->print_cr("Block until the serialize page permission restored");
   }
-  // When VMThread is holding the SerializePage_lock during modifying the
+  // When VMThread is holding the SerializePageLock during modifying the
   // access permission of the memory serialize page, the following call
   // will block until the permission of that page is restored to rw.
   // Generally, it is unsafe to manipulate locks in signal handlers, but in
   // this case, it's OK as the signal is synchronous and we know precisely when
-  // it can occur. SerializePage_lock is a transiently-held leaf lock, so
-  // lock_without_safepoint_check should be safe.
-  SerializePage_lock->lock_without_safepoint_check();
-  SerializePage_lock->unlock();
+  // it can occur.
+  Thread::muxAcquire(&SerializePageLock, "set_memory_serialize_page");
+  Thread::muxRelease(&SerializePageLock);
 }
 
 // Serialize all thread state variables
@@ -990,14 +990,12 @@
   // On some platforms such as Solaris & Linux, the time duration of the page
   // permission restoration is observed to be much longer than expected  due to
   // scheduler starvation problem etc. To avoid the long synchronization
-  // time and expensive page trap spinning, 'SerializePage_lock' is used to block
-  // the mutator thread if such case is encountered. Since this method is always
-  // called by VMThread during safepoint, lock_without_safepoint_check is used
-  // instead. See bug 6546278.
-  SerializePage_lock->lock_without_safepoint_check();
+  // time and expensive page trap spinning, 'SerializePageLock' is used to block
+  // the mutator thread if such case is encountered. See bug 6546278 for details.
+  Thread::muxAcquire(&SerializePageLock, "serialize_thread_states");
   os::protect_memory( (char *)os::get_memory_serialize_page(), os::vm_page_size() );
   os::unguard_memory( (char *)os::get_memory_serialize_page(), os::vm_page_size() );
-  SerializePage_lock->unlock();
+  Thread::muxRelease(&SerializePageLock);
 }
 
 // Returns true if the current stack pointer is above the stack shadow