RPC to self with rendez-vous leading to duplicate port destroy

[Samuel Thibault]

Hello,

I've investigated a duplicate port destroy in ext2fs, what apparently
happens is this:

- diskfs_S_dir_lookup is called, which for some reason ends up calling
- fshelp_fetch_root(), which calls
- reauth(), which calls
- mach_reply_port() to get a rendez-vous port, and then issues
- io_reauthenticate() with that port on ext2fs itself (since it's the
  root of the system), thus triggering a call to:
  - diskfs_S_io_reauthenticate() in another thread. There, the
  rendez-vous port is thus the same as the reply port obtained above,
  with the *same name*.
- reauth() destroys the rendez-vous port (and thus the name!)
  - a bit later, diskfs_S_io_reauthenticate has finished its work,
    and deallocates its rendez-vous port. But the name doesn't exist any
    more. Bad.

How are we supposed to deal with such case?

Samuel