x86, smpboot: Remove pointless preempt_disable() in native_smp_prepar…

…e_cpus()

There is no reason to keep preemption disabled in this function.

We only have two other threads live: kthreadd and idle. Neither of
them is going to preempt. But that preempt_disable forces all the code
inside to do GFP_ATOMIC allocations which is just insane.

Remove it.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Borislav Petkov <bp@alien8.de>
Cc: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: x86@kernel.org
Link: http://lkml.kernel.org/r/20141205084147.153643952@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/smpboot.c

@@ -1084,7 +1084,6 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
 {
  unsigned int i;
 
- preempt_disable();
  smp_cpu_index_default();
 
  /*
@@ -1102,22 +1101,19 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
  }
  set_cpu_sibling_map(0);
 
-
  if (smp_sanity_check(max_cpus) < 0) {
  pr_info("SMP disabled\n");
  disable_smp();
- goto out;
+ return;
  }
 
  default_setup_apic_routing();
 
- preempt_disable();
  if (read_apic_id() != boot_cpu_physical_apicid) {
  panic("Boot APIC ID in local APIC unexpected (%d vs %d)",
  read_apic_id(), boot_cpu_physical_apicid);
  /* Or can we switch back to PIC here? */
  }
- preempt_enable();
 
  connect_bsp_APIC();
 
@@ -1151,8 +1147,6 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
  uv_system_init();
 
  set_mtrr_aps_delayed_init();
-out:
- preempt_enable();
 }
 
 void arch_enable_nonboot_cpus_begin(void)