greybus: interface: prevent reactivation during removal

Make sure to prevent an interface that is going away from being
reactivated.

This is needed to preemptively close a race between the upcoming feature
to reactivate a powered-down interface and physical removal (i.e.
module_removed event processing) as well as logical removal (e.g. the
current system-suspend hack).
Reviewed-by: Sandeep Patil <sspatil@google.com>
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Reviewed-by: Alex Elder <elder@linaro.org>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Patrick Titiano <ptitiano@baylibre.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/interface.c

@@ -873,7 +873,7 @@ static int _gb_interface_activate(struct gb_interface *intf,
 
 	*type = GB_INTERFACE_TYPE_UNKNOWN;
 
-	if (intf->ejected)
+	if (intf->ejected || intf->removed)
 		return -ENODEV;
 
 	ret = gb_interface_vsys_set(intf, true);

drivers/staging/greybus/interface.h

@@ -53,6 +53,7 @@ struct gb_interface {
 	bool disconnected;
 
 	bool ejected;
+	bool removed;
 	bool active;
 	bool enabled;
 	bool mode_switch;

drivers/staging/greybus/module.c

@@ -186,6 +186,7 @@ static void gb_module_deregister_interface(struct gb_interface *intf)
 		intf->disconnected = true;
 
 	mutex_lock(&intf->mutex);
+	intf->removed = true;
 	gb_interface_disable(intf);
 	gb_interface_deactivate(intf);
 	mutex_unlock(&intf->mutex);