drivers/acpi/scan.c: document why we don't need the device_hotplug_lock

Let's document why the lock is not needed in acpi_scan_init(), right now
this is not really obvious.

[akpm@linux-foundation.org: fix tpyo]
Link: http://lkml.kernel.org/r/20190731135306.31524-1-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index 0e28270b0fd81046b2b2a434b0dd65edb4b282a6..aad6be5c0af0a5f4da721eed1fd8b77cd25f3b94 100644 (file)
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -2204,6 +2204,12 @@ int __init acpi_scan_init(void)
        acpi_gpe_apply_masked_gpes();
        acpi_update_all_gpes();
 
+       /*
+        * Although we call __add_memory() that is documented to require the
+        * device_hotplug_lock, it is not necessary here because this is an
+        * early code when userspace or any other code path cannot trigger
+        * hotplug/hotunplug operations.
+        */
        mutex_lock(&acpi_scan_lock);
        /*
         * Enumerate devices in the ACPI namespace.