RISC-V: Do not wait indefinitely in __cpu_up

In SMP path, __cpu_up waits for other CPU to come online indefinitely.
This is wrong as other CPU might be disabled in machine mode and
possible CPU is set to the cpus present in DT.

Introduce a completion variable and waits only for a second.
Signed-off-by: NAtish Patra <atish.patra@wdc.com>
Reviewed-by: NAnup Patel <anup@brainfault.org>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NPalmer Dabbelt <palmer@sifive.com>

arch/riscv/kernel/smpboot.c

@@ -39,6 +39,7 @@
 
 void *__cpu_up_stack_pointer[NR_CPUS];
 void *__cpu_up_task_pointer[NR_CPUS];
+static DECLARE_COMPLETION(cpu_running);
 
 void __init smp_prepare_boot_cpu(void)
 {
@@ -77,6 +78,7 @@ void __init setup_smp(void)
 
 int __cpu_up(unsigned int cpu, struct task_struct *tidle)
 {
+	int ret = 0;
 	int hartid = cpuid_to_hartid_map(cpu);
 	tidle->thread_info.cpu = cpu;
 
@@ -92,10 +94,16 @@ int __cpu_up(unsigned int cpu, struct task_struct *tidle)
 		  task_stack_page(tidle) + THREAD_SIZE);
 	WRITE_ONCE(__cpu_up_task_pointer[hartid], tidle);
 
-	while (!cpu_online(cpu))
-		cpu_relax();
+	lockdep_assert_held(&cpu_running);
+	wait_for_completion_timeout(&cpu_running,
+					    msecs_to_jiffies(1000));
 
-	return 0;
+	if (!cpu_online(cpu)) {
+		pr_crit("CPU%u: failed to come online\n", cpu);
+		ret = -EIO;
+	}
+
+	return ret;
 }
 
 void __init smp_cpus_done(unsigned int max_cpus)
@@ -121,6 +129,7 @@ asmlinkage void __init smp_callin(void)
 	 * a local TLB flush right now just in case.
 	 */
 	local_flush_tlb_all();
+	complete(&cpu_running);
 	/*
 	 * Disable preemption before enabling interrupts, so we don't try to
 	 * schedule a CPU that hasn't actually started yet.