ACPI: EC: Fix oops when removing custom query handlers

[ Upstream commit e5b492c ]

When removing custom query handlers, the handler might still
be used inside the EC query workqueue, causing a kernel oops
if the module holding the callback function was already unloaded.

Fix this by flushing the EC query workqueue when removing
custom query handlers.

Tested on a Acer Travelmate 4002WLMi

Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/acpi/ec.c

@@ -1122,6 +1122,7 @@ static void acpi_ec_remove_query_handlers(struct acpi_ec *ec,
 void acpi_ec_remove_query_handler(struct acpi_ec *ec, u8 query_bit)
 {
 	acpi_ec_remove_query_handlers(ec, false, query_bit);
+	flush_workqueue(ec_query_wq);
 }
 EXPORT_SYMBOL_GPL(acpi_ec_remove_query_handler);