x86, mce: fix a race condition about mce_callin and no_way_out

x86, mce: fix a race condition about mce_callin and no_way_out

If one CPU has no_way_out == 1, all other CPUs should have no_way_out
== 1. But despite global_nwo is read after mce_callin, global_nwo is
updated after mce_callin too. So it is possible that some CPU read
global_nwo before some other CPU update global_nwo, so that no_way_out
== 1 for some CPU, while no_way_out == 0 for some other CPU.

This patch fixes this race condition via moving mce_callin updating
after global_nwo updating, with a smp_wmb in between. A smp_rmb is
added between their reading too.

Signed-off-by: Huang Ying <ying.huang@intel.com>
Acked-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>