ACPICA: Mutex support: Fix release ordering issue and current sync level

Fixes a problem where if multiple mutexes of the same sync level
are acquired but then not released in strict opposite order, the
current sync level becomes confused and can cause errors.
ACPICA BZ 471.

http://acpica.org/bugzilla/show_bug.cgi?id=471

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/acpi/acpica/exmutex.c

@@ -83,6 +83,15 @@ void acpi_ex_unlink_mutex(union acpi_operand_object *obj_desc)
 
 	if (obj_desc->mutex.prev) {
 		(obj_desc->mutex.prev)->mutex.next = obj_desc->mutex.next;
+
+		/*
+		 * Migrate the previous sync level associated with this mutex to the
+		 * previous mutex on the list so that it may be preserved. This handles
+		 * the case where several mutexes have been acquired at the same level,
+		 * but are not released in opposite order.
+		 */
+		(obj_desc->mutex.prev)->mutex.original_sync_level =
+		    obj_desc->mutex.original_sync_level;
 	} else {
 		thread->acquired_mutex_list = obj_desc->mutex.next;
 	}
@@ -349,6 +358,7 @@ acpi_ex_release_mutex(union acpi_operand_object *obj_desc,
 		      struct acpi_walk_state *walk_state)
 {
 	acpi_status status = AE_OK;
+	u8 previous_sync_level;
 
 	ACPI_FUNCTION_TRACE(ex_release_mutex);
 
@@ -404,14 +414,21 @@ acpi_ex_release_mutex(union acpi_operand_object *obj_desc,
 		return_ACPI_STATUS(AE_AML_MUTEX_ORDER);
 	}
 
+	/*
+	 * Get the previous sync_level from the head of the acquired mutex list.
+	 * This handles the case where several mutexes at the same level have been
+	 * acquired, but are not released in reverse order.
+	 */
+	previous_sync_level =
+	    walk_state->thread->acquired_mutex_list->mutex.original_sync_level;
+
 	status = acpi_ex_release_mutex_object(obj_desc);
 
 	if (obj_desc->mutex.acquisition_depth == 0) {
 
 		/* Restore the original sync_level */
 
-		walk_state->thread->current_sync_level =
-		    obj_desc->mutex.original_sync_level;
+		walk_state->thread->current_sync_level = previous_sync_level;
 	}
 	return_ACPI_STATUS(status);
 }