start_kernel: test if irq's got enabled early, barf, and disable them again

The calls made by parse_parms to other initialization code might enable
interrupts again way too early.

Having interrupts on this early can make systems PANIC when they initialize
the IRQ controllers (which happens later in the code).  This patch detects
that irq's are enabled again, barfs about it and disables them again as a
safety net.

[akpm@osdl.org: cleanups]
Signed-off-by: Ard van Breemen <ard@telegraafnet.nl>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Adrian Bunk <bunk@stusta.de>

init/main.c

@@ -477,6 +477,11 @@ asmlinkage void __init start_kernel(void)
 	parse_args("Booting kernel", command_line, __start___param,
 		   __stop___param - __start___param,
 		   &unknown_bootoption);
+	if (!irqs_disabled()) {
+		printk(KERN_WARNING "start_kernel(): bug: interrupts were "
+				"enabled *very* early, fixing it\n");
+		local_irq_disable();
+	}
 	sort_main_extable();
 	trap_init();
 	rcu_init();