[PATCH AUTOSEL 4.9 44/68] ACPI / SBS: Fix rare oops when removing modules

[Sasha Levin <sashal@kernel.org>]

From: Ronald Tschalär <ronald@innovation.ch>

[ Upstream commit 757c968c442397f1249bb775a7c8c03842e3e0c7 ]

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 <ronald@innovation.ch>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/acpi/osl.c   | 1 +
 drivers/acpi/sbshc.c | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
index 416953a425109..b9fade7a3bcf4 100644
--- a/drivers/acpi/osl.c
+++ b/drivers/acpi/osl.c
@@ -1126,6 +1126,7 @@ 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;
diff --git a/drivers/acpi/sbshc.c b/drivers/acpi/sbshc.c
index 7a3431018e0ab..5008ead4609a4 100644
--- a/drivers/acpi/sbshc.c
+++ b/drivers/acpi/sbshc.c
@@ -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;
 }
 
@@ -292,6 +293,7 @@ static int acpi_smbus_hc_remove(struct acpi_device *device)
 
 	hc = acpi_driver_data(device);
 	acpi_ec_remove_query_handler(hc->ec, hc->query_bit);
+	acpi_os_wait_events_complete();
 	kfree(hc);
 	device->driver_data = NULL;
 	return 0;
-- 
2.20.1