x86: fix system without memory on node0

Jack found a boot crash on a system which doesn't have memory on node0.

It turns out with recent per_cpu changes, node_number for BSP will always
be 0, and it is not consistent to cpu_to_node() that might set it to a
different (nearer) node already.

aka when numa_set_node() for node0 is called early before per_cpu area is
setup:

two places touched that per_cpu(node_number,):

1. in cpu/common.c::cpu_init() and it is not for BP
| #ifdef CONFIG_NUMA
|        if (cpu != 0 && percpu_read(node_number) == 0 &&
|            cpu_to_node(cpu) != NUMA_NO_NODE)
|                percpu_write(node_number, cpu_to_node(cpu));
| #endif
for BP: traps_init ==> cpu_init
for AP: start_secondary ==> cpu_init

2. cpu/intel.c or amd.c::srat_detect_node via numa_set_node()
for BP: check_bugs ==> identify_boot_cpu ==> identify_cpu()
	 that is rather later before numa_node_id() is used for BP...
for AP: start_secondary => smp_callin => smp_store_cpu_info() =>
	=> identify_secondary_cpu => identify_cpu()

so try to set that for BP earlier in setup_per_cpu_areas(), and
don't bother to set that for APs there (it will be updated later
and will be used later)

(and don't mess the 0 before the copying BP per_cpu data to APs)

[ Impact: fix boot crash on memoryless node-0 ]

Reported-and-tested-by: Jack Steiner <steiner@sgi.com>
Cc: Tejun Heo <htejun@gmail.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <4A0C4A02.7050401@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/setup_percpu.c

@@ -423,6 +423,14 @@ void __init setup_per_cpu_areas(void)
 	early_per_cpu_ptr(x86_cpu_to_node_map) = NULL;
 #endif
 
+#if defined(CONFIG_X86_64) && defined(CONFIG_NUMA)
+	/*
+	 * make sure boot cpu node_number is right, when boot cpu is on the
+	 * node that doesn't have mem installed
+	 */
+	per_cpu(node_number, boot_cpu_id) = cpu_to_node(boot_cpu_id);
+#endif
+
 	/* Setup node to cpumask map */
 	setup_node_to_cpumask_map();