diff -r 0767c2f624c6 -r 63da8bd0c65e hgext/blackbox.py
--- a/hgext/blackbox.py	Tue Mar 08 20:52:57 2016 +0000
+++ b/hgext/blackbox.py	Tue Mar 08 20:34:59 2016 +0000
@@ -81,6 +81,7 @@
                 self._partialinit()
             else:
                 self._bbfp = src._bbfp
+                self._bbinlog = False
                 self._bbrepo = src._bbrepo
                 self._bbvfs = src._bbvfs
 
@@ -88,6 +89,7 @@
             if util.safehasattr(self, '_bbvfs'):
                 return
             self._bbfp = None
+            self._bbinlog = False
             self._bbrepo = None
             self._bbvfs = None
 
@@ -160,7 +162,15 @@
                 # was seen.
                 ui = lastui
 
-            if ui and ui._bbfp:
+            if not ui or not ui._bbfp:
+                return
+            if not lastui or ui._bbrepo:
+                lastui = ui
+            if ui._bbinlog:
+                # recursion guard
+                return
+            try:
+                ui._bbinlog = True
                 date = util.datestr(None, '%Y/%m/%d %H:%M:%S')
                 user = util.getuser()
                 pid = str(util.getpid())
@@ -186,11 +196,12 @@
                 except IOError as err:
                     self.debug('warning: cannot write to blackbox.log: %s\n' %
                                err.strerror)
-                if not lastui or ui._bbrepo:
-                    lastui = ui
+            finally:
+                ui._bbinlog = False
 
         def setrepo(self, repo):
             self._bbfp = None
+            self._bbinlog = False
             self._bbrepo = repo
             self._bbvfs = repo.vfs