From: Paolo 'Blaisorblade' Giarrusso <blaisorblade_spam@yahoo.it>
      Bodo Stroesser <bodo.stroesser@fujitsu-siemens.com>

While testing the host ptrace(2) features, we modify the stack frame of a test
child which is doing a syscall (namely getpid).  Either we override the
syscall number or the return value, which become the parent's pid, or we
don't, and the return value is the child's pid.

Actually, we only compared the return value with the child's pid, so we did
not notice a bug where the return value happened to be different from both.
So I added a stricter test here.
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade_spam@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>