JDK bug (conncurrent lock??)

I use ReentrantLock, but something strange happend. Locked..
(JDK 6 Update 6, Redhat Enterprise 3)

 class X {
   private final ReentrantLock lock = new ReentrantLock();
   // ...

   public void m() {
     lock.lock();  // block until condition holds
     try {
       // ... method body
     } finally {
       lock.unlock()
     }
   }

   public void n() {
     lock.lock();  // block until condition holds
     try {
       // ... method body
     } finally {
       lock.unlock()
     }
   }

 }
 

Like below, many thread locked by a 0x58266548 .

Many threads locked on the ReentrantLock instance.. So.. My clusion is "removing ReentrantLock instance" in my code. There are bug reports related with ReentrantLock in bug.sun.com and web..

I changed "lock" to synchronized..

"Worker-17" prio=10 tid=0x4c504400 nid=0x1179 waiting on condition [0x490be000..0x490beea0]
   java.lang.Thread.State: WAITING (parking)
    at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <0x58266548> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:158)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:747)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:778)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1114)
    at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:186)
    at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:262)
.. my package-source...