After VFS shutdown, init(8) cannot map a missing page that contains

After VFS shutdown, init(8) cannot map a missing page that contains
the signal handler code.  Traditionally a process would spin in
such a case, but we changed the logic in revision 1.167 trapsignal()
to receive a fatal signal.  If that happens to init(8), the kernel
panics.  In case of reboot, jump between init signal handler and
page fault trap until the kernel resets the machine.
reported and tested weerd@; OK deraadt@