title: Debug a futex lock
body: <p>I have a process waiting on a futex:</p>
  
  <pre><code># strace -p 5538
  Process 5538 attached - interrupt to quit
  futex(0x7f86c9ed6a0c, FUTEX_WAIT, 20, NULL
  </code></pre>
  
  <p>How can I best debug such a situation? Can I identify who holds the futex? Are there any tools similar to ipcs and ipcrm but for futexes?</p>