usb: gadget: u_ether: Add auto-cleanup helper for freeing net_device

[ Upstream commit 0c09811 ]

The net_device in the u_ether framework currently requires explicit
calls to unregister and free the device.

Introduce gether_unregister_free_netdev() and the corresponding
auto-cleanup macro. This ensures that if a net_device is registered, it
is properly unregistered and the associated work queue is flushed before
the memory is freed.

This is a preparatory patch to simplify error handling paths in gadget
drivers by removing the need for explicit goto labels for net_device
cleanup.

Signed-off-by: Kuen-Han Tsai <khtsai@google.com>
Link: https://patch.msgid.link/20251230-ncm-refactor-v1-2-793e347bc7a7@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Stable-dep-of: 56a512a ("usb: gadget: f_ncm: align net_device lifecycle with bind/unbind")
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Kuen-Han Tsai

drivers/usb/gadget/function/u_ether.c

@@ -1125,6 +1125,21 @@ void gether_cleanup(struct eth_dev *dev)
 }
 EXPORT_SYMBOL_GPL(gether_cleanup);
 
+void gether_unregister_free_netdev(struct net_device *net)
+{
+	if (!net)
+		return;
+
+	struct eth_dev *dev = netdev_priv(net);
+
+	if (net->reg_state == NETREG_REGISTERED) {
+		unregister_netdev(net);
+		flush_work(&dev->work);
+	}
+	free_netdev(net);
+}
+EXPORT_SYMBOL_GPL(gether_unregister_free_netdev);
+
 /**
  * gether_connect - notify network layer that USB link is active
  * @link: the USB link, set up with endpoints, descriptors matching

drivers/usb/gadget/function/u_ether.h

@@ -283,6 +283,8 @@ int gether_get_ifname(struct net_device *net, char *name, int len);
 int gether_set_ifname(struct net_device *net, const char *name, int len);
 
 void gether_cleanup(struct eth_dev *dev);
+void gether_unregister_free_netdev(struct net_device *net);
+DEFINE_FREE(free_gether_netdev, struct net_device *, gether_unregister_free_netdev(_T));
 
 void gether_setup_opts_default(struct gether_opts *opts, const char *name);
 void gether_apply_opts(struct net_device *net, struct gether_opts *opts);