ACPI: processor: idle: Fix NULL pointer dereference in hotplug path

A cpuidle_device might fail to register during boot, but the system can
continue to run. In such cases, acpi_processor_hotplug() can trigger
a NULL pointer dereference when accessing the per-cpu acpi_cpuidle_device.

So add NULL pointer check for the per-cpu acpi_cpuidle_device in
acpi_processor_hotplug.

Signed-off-by: Huisong Li <lihuisong@huawei.com>
Link: https://patch.msgid.link/20260403090253.998322-1-lihuisong@huawei.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: LiHuiSong1

drivers/acpi/processor_idle.c

@@ -1267,16 +1267,15 @@ static int acpi_processor_get_power_info(struct acpi_processor *pr)
 
 int acpi_processor_hotplug(struct acpi_processor *pr)
 {
+	struct cpuidle_device *dev = per_cpu(acpi_cpuidle_device, pr->id);
 	int ret = 0;
-	struct cpuidle_device *dev;
 
 	if (disabled_by_idle_boot_param())
 		return 0;
 
-	if (!pr->flags.power_setup_done)
+	if (!pr->flags.power_setup_done || !dev)
 		return -ENODEV;
 
-	dev = per_cpu(acpi_cpuidle_device, pr->id);
 	cpuidle_pause_and_lock();
 	cpuidle_disable_device(dev);
 	ret = acpi_processor_get_power_info(pr);