[PATCH v1] drivers/acpi/scan.c: Fixup "acquire device_hotplug_lock in acpi_scan_init()"

[David Hildenbrand <david@redhat.com>]

Let's document why we take the lock here. If we're going to overhaul
memory hotplug locking, we'll have to touch many places - this comment
will help to clairfy why it was added here.

Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 drivers/acpi/scan.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index cbc9d64b48dd..9193f1d46148 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -2204,6 +2204,11 @@ int __init acpi_scan_init(void)
 	acpi_gpe_apply_masked_gpes();
 	acpi_update_all_gpes();
 
+	/*
+	 * We end up calling __add_memory(), which expects the
+	 * device_hotplug_lock to be held. Races with userspace and other
+	 * hotplug activities are not really possible - lock for consistency.
+	 */
 	lock_device_hotplug();
 	mutex_lock(&acpi_scan_lock);
 
-- 
2.21.0