Comment 9 for bug 1465322

Here's some more detail:

running 'strace df' shows the following:

  statfs64("/sys/kernel/debug", 84, 0xbfddc6bc) = -1 ENOSYS (Function not implemented)

A quick test shows that adding '.statfs = simple_statfs' in the debugfs_super_operations struct fixes the problem, but I'm not sure
that's the right thing to do.

(This has been reported upstream: http://thread.gmane.org/gmane.linux.kernel.stable/134708/focus=134588)