Commit 7ad728f98162cb1af06a85b2a5fc422dddd4fb78
(cpumask: x86: convert cpu_sibling_map/cpu_core_map to cpumask_var_t)
changed the output of /proc/cpuinfo for siblings:

Example on an AMD Phenom:

  physical id   : 0
  siblings : 1
  core id	   : 3
  cpu cores  : 4

Before that commit it was:

  physical id	: 0
  siblings : 4
  core id	   : 3
  cpu cores  : 4

Instead of cpu_core_mask it now uses cpu_sibling_mask to count siblings.
This is due to the following hunk of above commit:

|  --- a/arch/x86/kernel/cpu/proc.c
|  +++ b/arch/x86/kernel/cpu/proc.c
|  @@ -14,7 +14,7 @@ static void show_cpuinfo_core(struct seq_file *m, struct cpuinf
|          if (c->x86_max_cores * smp_num_siblings > 1) {
|                  seq_printf(m, "physical id\t: %d\n", c->phys_proc_id);
|                  seq_printf(m, "siblings\t: %d\n",
|  -                          cpus_weight(per_cpu(cpu_core_map, cpu)));
|  +                          cpumask_weight(cpu_sibling_mask(cpu)));
|                  seq_printf(m, "core id\t\t: %d\n", c->cpu_core_id);
|                  seq_printf(m, "cpu cores\t: %d\n", c->booted_cores);
|                  seq_printf(m, "apicid\t\t: %d\n", c->apicid);

This was a mistake, because the impact line shows that this side-effect
was not anticipated:

   Impact: reduce per-cpu size for CONFIG_CPUMASK_OFFSTACK=y

So revert the respective hunk to restore the old behavior.

[ Impact: fix sibling-info regression in /proc/cpuinfo ]

Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
LKML-Reference: <20090504182859.GA29045@alberich.amd.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>