the paravirt-spinlock patches caused a boot hang with this config:

 http://redhat.com/~mingo/misc/config-Wed_Jul__9_14_47_04_CEST_2008.bad



i have bisected it down to:

|  commit e17b58c2e85bc2ad2afc07fb8d898017c2b75ed1
|  Author: Jeremy Fitzhardinge <jeremy@goop.org>
|  Date:   Mon Jul 7 12:07:53 2008 -0700
|
|      xen: implement Xen-specific spinlocks

i.e. applying that patch alone causes the hang. The hang happens in the
ftrace self-test:

  initcall utsname_sysctl_init+0x0/0x19 returned 0 after 0 msecs
  calling  init_sched_switch_trace+0x0/0x4c
  Testing tracer sched_switch: PASSED
  initcall init_sched_switch_trace+0x0/0x4c returned 0 after 167 msecs
  calling  init_function_trace+0x0/0x12
  Testing tracer ftrace:
  [hard hang]

it should have continued like this:

  Testing tracer ftrace: PASSED
  initcall init_function_trace+0x0/0x12 returned 0 after 198 msecs
  calling  init_irqsoff_tracer+0x0/0x14
  Testing tracer irqsoff: PASSED
  initcall init_irqsoff_tracer+0x0/0x14 returned 0 after 3 msecs
  calling  init_mmio_trace+0x0/0x12
  initcall init_mmio_trace+0x0/0x12 returned 0 after 0 msecs

the problem is that such lowlevel primitives as spinlocks should never
be built with -pg (which ftrace does). Marking paravirt.o as non-pg and
marking all spinlock ops as always-inline solve the hang.

Signed-off-by: Ingo Molnar <mingo@elte.hu>