[PATCH] arm64/kernel: Simplify __cpu_up() by bailing out early

[Gavin Shan <gshan@redhat.com>]

The function __cpu_up() is invoked to bring up the target CPU through
the backend, PSCI for example. The nested if statements won't be needed
if we bail out early on the following two conditions where the status
won't be checked. The code looks simplified in that case.

   * Error returned from the backend (e.g. PSCI)
   * The target CPU has been marked as onlined

Signed-off-by: Gavin Shan <gshan@redhat.com>
---
 arch/arm64/kernel/smp.c | 79 +++++++++++++++++++----------------------
 1 file changed, 37 insertions(+), 42 deletions(-)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index d4ed9a19d8fe..2a9d8f39dc58 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -115,60 +115,55 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
 	update_cpu_boot_status(CPU_MMU_OFF);
 	__flush_dcache_area(&secondary_data, sizeof(secondary_data));
 
-	/*
-	 * Now bring the CPU into our world.
-	 */
+	/* Now bring the CPU into our world */
 	ret = boot_secondary(cpu, idle);
-	if (ret == 0) {
-		/*
-		 * CPU was successfully started, wait for it to come online or
-		 * time out.
-		 */
-		wait_for_completion_timeout(&cpu_running,
-					    msecs_to_jiffies(5000));
-
-		if (!cpu_online(cpu)) {
-			pr_crit("CPU%u: failed to come online\n", cpu);
-			ret = -EIO;
-		}
-	} else {
+	if (ret) {
 		pr_err("CPU%u: failed to boot: %d\n", cpu, ret);
 		return ret;
 	}
 
+	/*
+	 * CPU was successfully started, wait for it to come online or
+	 * time out.
+	 */
+	wait_for_completion_timeout(&cpu_running,
+				    msecs_to_jiffies(5000));
+	if (cpu_online(cpu))
+		return 0;
+
+	pr_crit("CPU%u: failed to come online\n", cpu);
 	secondary_data.task = NULL;
 	secondary_data.stack = NULL;
 	__flush_dcache_area(&secondary_data, sizeof(secondary_data));
 	status = READ_ONCE(secondary_data.status);
-	if (ret && status) {
-
-		if (status == CPU_MMU_OFF)
-			status = READ_ONCE(__early_cpu_boot_status);
+	if (status == CPU_MMU_OFF)
+		status = READ_ONCE(__early_cpu_boot_status);
 
-		switch (status & CPU_BOOT_STATUS_MASK) {
-		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)) {
-				pr_crit("CPU%u: died during early boot\n", cpu);
-				break;
-			}
-			pr_crit("CPU%u: may not have shut down cleanly\n", cpu);
-			/* Fall through */
-		case CPU_STUCK_IN_KERNEL:
-			pr_crit("CPU%u: is stuck in kernel\n", cpu);
-			if (status & CPU_STUCK_REASON_52_BIT_VA)
-				pr_crit("CPU%u: does not support 52-bit VAs\n", cpu);
-			if (status & CPU_STUCK_REASON_NO_GRAN)
-				pr_crit("CPU%u: does not support %luK granule \n", cpu, PAGE_SIZE / SZ_1K);
-			cpus_stuck_in_kernel++;
+	switch (status & CPU_BOOT_STATUS_MASK) {
+	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)) {
+			pr_crit("CPU%u: died during early boot\n", cpu);
 			break;
-		case CPU_PANIC_KERNEL:
-			panic("CPU%u detected unsupported configuration\n", cpu);
 		}
+		pr_crit("CPU%u: may not have shut down cleanly\n", cpu);
+		/* Fall through */
+	case CPU_STUCK_IN_KERNEL:
+		pr_crit("CPU%u: is stuck in kernel\n", cpu);
+		if (status & CPU_STUCK_REASON_52_BIT_VA)
+			pr_crit("CPU%u: does not support 52-bit VAs\n", cpu);
+		if (status & CPU_STUCK_REASON_NO_GRAN) {
+			pr_crit("CPU%u: does not support %luK granule\n",
+				cpu, PAGE_SIZE / SZ_1K);
+		}
+		cpus_stuck_in_kernel++;
+		break;
+	case CPU_PANIC_KERNEL:
+		panic("CPU%u detected unsupported configuration\n", cpu);
 	}
 
 	return ret;
-- 
2.23.0