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>

1 files changed, 13 insertions, 8 deletions

diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
index 7dfe91d0173e..6dc4a2b1e956 100644
--- 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