ACPI: Make seemingly useless check in osl.c more understandable

There is a seemingly useless check in drivers/acpi/osl.c added by
commit bc73675 (ACPI: fixes a false alarm from lockdep), which really
is necessary to avoid false positive lockdep complaints.  Document
this and rearrange the code related to it so that it makes fewer
checks.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>

diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
index 7dfe91d..6dc4a2b 100644 (file)
--- a/drivers/acpi/osl.c
+++ b/drivers/acpi/osl.c
@@ -932,7 +932,7 @@ static acpi_status __acpi_os_execute(acpi_execute_type type,
         * having a static work_struct.
         */
 
-       dpc = kmalloc(sizeof(struct acpi_os_dpc), GFP_ATOMIC);
+       dpc = kzalloc(sizeof(struct acpi_os_dpc), GFP_ATOMIC);
        if (!dpc)
                return AE_NO_MEMORY;
 
@@ -944,17 +944,22 @@ static acpi_status __acpi_os_execute(acpi_execute_type type,
         * because the hotplug code may call driver .remove() functions,
         * which invoke flush_scheduled_work/acpi_os_wait_events_complete
         * to flush these workqueues.
+        *
+        * To prevent lockdep from complaining unnecessarily, make sure that
+        * there is a different static lockdep key for each workqueue by using
+        * INIT_WORK() for each of them separately.
         */
-       queue = hp ? kacpi_hotplug_wq :
-               (type == OSL_NOTIFY_HANDLER ? kacpi_notify_wq : kacpid_wq);
-       dpc->wait = hp ? 1 : 0;
-
-       if (queue == kacpi_hotplug_wq)
+       if (hp) {
+               queue = kacpi_hotplug_wq;
+               dpc->wait = 1;
                INIT_WORK(&dpc->work, acpi_os_execute_deferred);
-       else if (queue == kacpi_notify_wq)
+       } else if (type == OSL_NOTIFY_HANDLER) {
+               queue = kacpi_notify_wq;
                INIT_WORK(&dpc->work, acpi_os_execute_deferred);
-       else
+       } else {
+               queue = kacpid_wq;
                INIT_WORK(&dpc->work, acpi_os_execute_deferred);
+       }
 
        /*
         * On some machines, a software-initiated SMI causes corruption unless