sched/x86/smp: Do not enable IRQs over calibrate_delay()

We should not ever enable IRQs until we're fully set up. This opens up
a window where interrupts can hit the cpu and interrupts can do
wakeups, wakeups need state that isn't set-up yet, in particular this
cpu isn't elegible to run tasks, so if any cpu-affine task that got
created in CPU_UP_PREPARE manages to get a wakeup, its affinity mask
will get broken and we'll run into lots of 'interesting' problems.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-yaezmlbriluh166tfkgni22m@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/smpboot.c

@@ -219,14 +219,9 @@ static void __cpuinit smp_callin(void)
 	 * Update loops_per_jiffy in cpu_data. Previous call to
 	 * smp_store_cpu_info() stored a value that is close but not as
 	 * accurate as the value just calculated.
-	 *
-	 * Need to enable IRQs because it can take longer and then
-	 * the NMI watchdog might kill us.
 	 */
-	local_irq_enable();
 	calibrate_delay();
 	cpu_data(cpuid).loops_per_jiffy = loops_per_jiffy;
-	local_irq_disable();
 	pr_debug("Stack at about %p\n", &cpuid);
 
 	/*