arm64: smp: Treat unknown boot failures as being 'stuck in kernel'

When we fail to bring a secondary CPU online and it fails in an unknown
state, we should assume the worst and increment 'cpus_stuck_in_kernel'
so that things like kexec() are disabled.

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/kernel/smp.c

@@ -147,6 +147,7 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
 		default:
 			pr_err("CPU%u: failed in unknown state : 0x%lx\n",
 					cpu, status);
+			cpus_stuck_in_kernel++;
 			break;
 		case CPU_KILL_ME:
 			if (!op_cpu_kill(cpu)) {