x86: disable preemption in native_smp_prepare_cpus

Priit Laes reported the following warning:

Call Trace:
 [<ffffffff8022f1e1>] warn_on_slowpath+0x51/0x63
 [<ffffffff80282e48>] sys_ioctl+0x2d/0x5d
 [<ffffffff805185ff>] _spin_lock+0xe/0x24
 [<ffffffff80227459>] task_rq_lock+0x3d/0x73
 [<ffffffff805133c3>] set_cpu_sibling_map+0x336/0x350
 [<ffffffff8021c1b8>] read_apic_id+0x30/0x62
 [<ffffffff806d921d>] verify_local_APIC+0x90/0x138
 [<ffffffff806d84b5>] native_smp_prepare_cpus+0x1f9/0x305
 [<ffffffff806ce7b1>] kernel_init+0x59/0x2d9
 [<ffffffff80518a26>] _spin_unlock_irq+0x11/0x2b
 [<ffffffff8020bf48>] child_rip+0xa/0x12
 [<ffffffff806ce758>] kernel_init+0x0/0x2d9
 [<ffffffff8020bf3e>] child_rip+0x0/0x12

fix this by generally disabling preemption in native_smp_prepare_cpus().
Reported-and-bisected-by: Priit Laes <plaes@plaes.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/smpboot.c

@@ -1190,6 +1190,7 @@ static void __init smp_cpu_index_default(void)
  */
 void __init native_smp_prepare_cpus(unsigned int max_cpus)
 {
+	preempt_disable();
 	nmi_watchdog_default();
 	smp_cpu_index_default();
 	current_cpu_data = boot_cpu_data;
@@ -1206,7 +1207,7 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
 	if (smp_sanity_check(max_cpus) < 0) {
 		printk(KERN_INFO "SMP disabled\n");
 		disable_smp();
-		return;
+		goto out;
 	}
 
 	preempt_disable();
@@ -1246,6 +1247,8 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
 	printk(KERN_INFO "CPU%d: ", 0);
 	print_cpu_info(&cpu_data(0));
 	setup_boot_clock();
+out:
+	preempt_enable();
 }
 /*
  * Early setup to make printk work.