x86: idle process - add checking for NULL early param

Signed-off-by: NCyrill Gorcunov <gorcunov@gmail.com>
Cc: akpm@linux-foundation.org
Cc: andi@firstfloor.org
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/process.c

@@ -164,6 +164,9 @@ void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)
 
 static int __init idle_setup(char *str)
 {
+	if (!str)
+		return -EINVAL;
+
 	if (!strcmp(str, "poll")) {
 		printk("using polling idle threads.\n");
 		pm_idle = poll_idle;