net: add granular lock for the netdev netlink socket

As we move away from rtnl_lock for queue ops, introduce
per-netdev_nl_sock lock.

Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
Reviewed-by: Mina Almasry <almasrymina@google.com>
Link: https://patch.msgid.link/20250311144026.4154277-3-sdf@fomichev.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/netdev_netlink.h

@@ -5,6 +5,7 @@
 #include <linux/list.h>
 
 struct netdev_nl_sock {
+	struct mutex lock;
 	struct list_head bindings;
 };
 

net/core/netdev-genl.c

@@ -859,6 +859,7 @@ int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
 		goto err_genlmsg_free;
 	}
 
+	mutex_lock(&priv->lock);
 	rtnl_lock();
 
 	netdev = __dev_get_by_index(genl_info_net(info), ifindex);
@@ -918,13 +919,15 @@ int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
 		goto err_unbind;
 
 	rtnl_unlock();
+	mutex_unlock(&priv->lock);
 
 	return 0;
 
 err_unbind:
 	net_devmem_unbind_dmabuf(binding);
 err_unlock:
 	rtnl_unlock();
+	mutex_unlock(&priv->lock);
 err_genlmsg_free:
 	nlmsg_free(rsp);
 	return err;
@@ -933,18 +936,21 @@ int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
 void netdev_nl_sock_priv_init(struct netdev_nl_sock *priv)
 {
 	INIT_LIST_HEAD(&priv->bindings);
+	mutex_init(&priv->lock);
 }
 
 void netdev_nl_sock_priv_destroy(struct netdev_nl_sock *priv)
 {
 	struct net_devmem_dmabuf_binding *binding;
 	struct net_devmem_dmabuf_binding *temp;
 
+	mutex_lock(&priv->lock);
 	list_for_each_entry_safe(binding, temp, &priv->bindings, list) {
 		rtnl_lock();
 		net_devmem_unbind_dmabuf(binding);
 		rtnl_unlock();
 	}
+	mutex_unlock(&priv->lock);
 }
 
 static int netdev_genl_netdevice_event(struct notifier_block *nb,