smp_call_function_single with wait=0 considered harmful

[Christoph Hellwig <hch@infradead.org>]

While doing my recent work on the generic smp function calls I noticed
that smp_call_function_single without the wait flag can't work, as
it allocates struct call_single_data on stack, and without the wait
flag will happily return before the IPI has been executed.

This affects the following callers:

  arch/ia64/kernel/mca.c:mca_cpu_callback()
  arch/ia64/kernel/smpboot.c:ia64_sync_itc()
  arch/x86/kernel/kvm.c:kvm_cpu_notify()
  arch/x86/oprofile/nmi_int.c:oprofile_cpu_notifier()
  arch/x86/pci/amd_bus.c:amd_cpu_notify()
  drivers/staging/octeon/ethernet-rx.c:cvm_oct_enable_one_cpu()
  kernel/stop_machine.c:stop_two_cpus()

It would be good to get these fixed so that we could remove the
parameter.  Either convert them to wait, or use a preallocated
call_single_data and __smp_call_function_single.

After that I'd like to remove the wait argument to prevent further
abuses.