Builds fail in mock ccache plugin setup

[euanh]

03:21:32.838 ERROR: Exception(SRPMS/ocaml-typerep-111.17.00-1.el6.src.rpm) Config(epel-6-x86_64) 0 minutes 7 seconds
03:21:33.166 Traceback (most recent call last):
03:21:33.166 File "/usr/sbin/mock", line 829, in
03:21:33.166 main()
03:21:33.167 File "/usr/lib/python2.6/site-packages/mockbuild/trace_decorator.py", line 84, in trace

03:21:33.168     result = func(*args, **kw)
03:21:33.168   File "/usr/sbin/mock", line 650, in main
03:21:33.168     run_command(options, args, config_opts, commands, buildroot, state)
03:21:33.168   File "/usr/lib/python2.6/site-packages/mockbuild/trace_decorator.py", line 84, in trace
03:21:33.168     result = func(*args, **kw)
03:21:33.168   File "/usr/sbin/mock", line 725, in run_command
03:21:33.168     do_rebuild(config_opts, commands, buildroot, args)
03:21:33.169   File "/usr/lib/python2.6/site-packages/mockbuild/trace_decorator.py", line 84, in trace
03:21:33.169     result = func(*args, **kw)
03:21:33.169   File "/usr/sbin/mock", line 496, in do_rebuild
03:21:33.170     post=post_build, clean=clean)
03:21:33.170   File "/usr/lib/python2.6/site-packages/mockbuild/trace_decorator.py", line 84, in trace
03:21:33.170     result = func(*args, **kw)
03:21:33.170   File "/usr/sbin/mock", line 440, in rebuild_generic
03:21:33.170     commands.init(prebuild=not config_opts.get('short_circuit'))
03:21:33.170   File "/usr/lib/python2.6/site-packages/mockbuild/trace_decorator.py", line 84, in trace
03:21:33.170     result = func(*args, **kw)
03:21:33.170   File "/usr/lib/python2.6/site-packages/mockbuild/backend.py", line 122, in init
03:21:33.170     self.buildroot.initialize(**kwargs)
03:21:33.170   File "/usr/lib/python2.6/site-packages/mockbuild/trace_decorator.py", line 84, in trace
03:21:33.170     result = func(*args, **kw)
03:21:33.170   File "/usr/lib/python2.6/site-packages/mockbuild/buildroot.py", line 80, in initialize
03:21:33.170     self._init(prebuild=prebuild, do_log=do_log)
03:21:33.170   File "/usr/lib/python2.6/site-packages/mockbuild/trace_decorator.py", line 84, in trace
03:21:33.170     result = func(*args, **kw)
03:21:33.170   File "/usr/lib/python2.6/site-packages/mockbuild/buildroot.py", line 117, in _init
03:21:33.170     self.plugins.call_hooks('preinit')
03:21:33.170   File "/usr/lib/python2.6/site-packages/mockbuild/trace_decorator.py", line 84, in trace
03:21:33.171     result = func(*args, **kw)
03:21:33.171   File "/usr/lib/python2.6/site-packages/mockbuild/plugin.py", line 65, in call_hooks
03:21:33.171     hook(*args, **kwargs)
03:21:33.172   File "/usr/lib/python2.6/site-packages/mockbuild/trace_decorator.py", line 84, in trace
03:21:33.172     result = func(*args, **kw)
03:21:33.172   File "/usr/lib/python2.6/site-packages/mockbuild/plugins/ccache.py", line 60, in _ccachePreInitHook
03:21:33.172     self.buildroot.uid_manager.changeOwner(self.ccachePath, recursive=True)
03:21:33.172   File "/usr/lib/python2.6/site-packages/mockbuild/trace_decorator.py", line 84, in trace
03:21:33.172     result = func(*args, **kw)
03:21:33.172   File "/usr/lib/python2.6/site-packages/mockbuild/uid.py", line 84, in changeOwner
03:21:33.172     os.chown(os.path.join(root, f), uid, gid)
03:21:33.172 OSError: [Errno 2] No such file or directory: '/var/cache/mock/epel-6-x86_64/ccache/u500/b/stats.lock'
03:21:33.281 make: *** [RPMS/x86_64/ocaml-typerep-111.17.00-1.el6.x86_64.rpm] Error 1
03:21:33.281 make: *** Waiting for unfinished jobs....

Google reveals a few similar reports, but not many. Until we can figure out the real cause, may be best to disable the ccache plugin in the mock configuration.