irq/core: Fix boot crash when the irqaffinity= boot parameter is passed on CPUMASK_OFFSTACK=y kernels(v1)

When the irqaffinity= kernel parameter is passed in a CPUMASK_OFFSTACK=y
kernel, it fails to boot, because zalloc_cpumask_var() cannot be used before
initializing the slab allocator to allocate a cpumask.

So, use alloc_bootmem_cpumask_var() instead.

Also do some cleanups while at it: in init_irq_default_affinity() remove
an #ifdef via using cpumask_available().

Signed-off-by: Rakib Mullick <rakib.mullick@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20171026045800.27087-1-rakib.mullick@gmail.com
Link: http://lkml.kernel.org/r/20171101041451.12581-1-rakib.mullick@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/irq/irqdesc.c

@@ -27,7 +27,7 @@ static struct lock_class_key irq_desc_lock_class;
 #if defined(CONFIG_SMP)
 static int __init irq_affinity_setup(char *str)
 {
-	zalloc_cpumask_var(&irq_default_affinity, GFP_NOWAIT);
+	alloc_bootmem_cpumask_var(&irq_default_affinity);
 	cpulist_parse(str, irq_default_affinity);
 	/*
 	 * Set at least the boot cpu. We don't want to end up with
@@ -40,10 +40,8 @@ __setup("irqaffinity=", irq_affinity_setup);
 
 static void __init init_irq_default_affinity(void)
 {
-#ifdef CONFIG_CPUMASK_OFFSTACK
-	if (!irq_default_affinity)
+	if (!cpumask_available(irq_default_affinity))
 		zalloc_cpumask_var(&irq_default_affinity, GFP_NOWAIT);
-#endif
 	if (cpumask_empty(irq_default_affinity))
 		cpumask_setall(irq_default_affinity);
 }