greybus: core: add defensive connection disable post disconnect

Bundle drivers *must* disable their connections in the disconnect
callback, but add a defensive test and warn about buggy drivers
nonetheless.

Note that bundle drivers would generally release their state containers
in disconnect so a failure stop I/O could potentially lead to
use-after-free bugs in any late operation completion callbacks.
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/core.c

@@ -165,6 +165,13 @@ static int greybus_remove(struct device *dev)
 		gb_connection_disable_rx(connection);
 
 	driver->disconnect(bundle);
+
+	/* Catch buggy drivers that fail to disable their connections. */
+	list_for_each_entry(connection, &bundle->connections, bundle_links) {
+		if (WARN_ON(connection->state != GB_CONNECTION_STATE_DISABLED))
+			gb_connection_disable(connection);
+	}
+
 	return 0;
 }