ACPI/sbshc: Fix rare oops when removing modules.

There was a small race when removing the sbshc module where smbus_alarm() had queued acpi_smbus_callback() for deferred execution but it hadn't been run yet, so that when it did run hc had been freed and the module unloaded, resulting in an invalid paging request.

A similar race existed when removing the sbs module with regards to acpi_sbs_callback() (which is called from acpi_smbus_callback()).

We therefore need to ensure no callbacks are pending or executing before the cleanups are done and the modules are removed.

Signed-off-by Ronald Tschalär <[email protected]>

---
 drivers/acpi/osl.c   | 1 +
 drivers/acpi/sbshc.c | 2 ++
 2 files changed, 3 insertions(+)

drivers/acpi/osl.c +1 -0

index 8df9abfa947b..9d139727f164 100644
@@ -1129,6 +1129,7 @@ void acpi_os_wait_events_complete(void)
 	flush_workqueue(kacpid_wq);
 	flush_workqueue(kacpi_notify_wq);
 }
+EXPORT_SYMBOL(acpi_os_wait_events_complete);
 
 struct acpi_hp_work {
 	struct work_struct work;

drivers/acpi/sbshc.c +1 -0

index 7a3431018e0a..5008ead4609a 100644
@@ -196,6 +196,7 @@ int acpi_smbus_unregister_callback(struct acpi_smb_hc *hc)
 	hc->callback = NULL;
 	hc->context = NULL;
 	mutex_unlock(&hc->lock);
+	acpi_os_wait_events_complete();
 	return 0;
 }