x86_64: oops_begin() fix

We don't want to see this:

>  BUG: using smp_processor_id() in preemptible [00000001] code: bash/3857
>  caller is oops_begin+0xb/0x6f
>
>  Call Trace:
>  [<ffffffff8020ab4d>] show_trace+0x34/0x4f
>  [<ffffffff8020ab7a>] dump_stack+0x12/0x17
>  [<ffffffff8030d92d>] debug_smp_processor_id+0xad/0xbc
>  [<ffffffff8042388f>] oops_begin+0xb/0x6f
>  [<ffffffff8042520b>] do_page_fault+0x66a/0x7c0
>  [<ffffffff804234bd>] error_exit+0x0/0x84
>

coming out when the kernel is trying to oops.

Cc: Andi Kleen <ak@suse.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/x86_64/kernel/traps.c

@@ -465,13 +465,14 @@ static unsigned int die_nest_count;
 
 unsigned __kprobes long oops_begin(void)
 {
-	int cpu = smp_processor_id();
+	int cpu;
 	unsigned long flags;
 
 	oops_enter();
 
 	/* racy, but better than risking deadlock. */
 	local_irq_save(flags);
+	cpu = smp_processor_id();
 	if (!spin_trylock(&die_lock)) { 
 		if (cpu == die_owner) 
 			/* nested oops. should stop eventually */;