--- a/mercurial/lock.py	Sun Mar 27 21:05:55 2016 +0900
+++ b/mercurial/lock.py	Sat Apr 16 09:00:15 2016 -0700
@@ -234,6 +234,8 @@
             if not self._parentheld:
                 for callback in self.postrelease:
                     callback()
+                # Prevent double usage and help clear cycles.
+                self.postrelease = None
 
 def release(*locks):
     for lock in locks: