net: remove init_dummy_netdev()

init_dummy_netdev() can initialize statically declared or embedded
net_devices. Such netdevs did not come from alloc_netdev_mqs().
After recent work by Breno, there are the only two cases where
we have do that.

Switch those cases to alloc_netdev_mqs() and delete init_dummy_netdev().
Dealing with static netdevs is not worth the maintenance burden.

Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Reviewed-by: Joe Damato <jdamato@fastly.com>
Link: https://patch.msgid.link/20250113003456.3904110-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/netdevice.h

@@ -3238,7 +3238,6 @@ static inline void unregister_netdevice(struct net_device *dev)
 
 int netdev_refcnt_read(const struct net_device *dev);
 void free_netdev(struct net_device *dev);
-void init_dummy_netdev(struct net_device *dev);
 
 struct net_device *netdev_get_xmit_slave(struct net_device *dev,
 					 struct sk_buff *skb,

net/core/dev.c

@@ -10762,28 +10762,6 @@ static void init_dummy_netdev_core(struct net_device *dev)
 	 */
 }
 
-/**
- *	init_dummy_netdev	- init a dummy network device for NAPI
- *	@dev: device to init
- *
- *	This takes a network device structure and initializes the minimum
- *	amount of fields so it can be used to schedule NAPI polls without
- *	registering a full blown interface. This is to be used by drivers
- *	that need to tie several hardware interfaces to a single NAPI
- *	poll scheduler due to HW limitations.
- */
-void init_dummy_netdev(struct net_device *dev)
-{
-	/* Clear everything. Note we don't initialize spinlocks
-	 * as they aren't supposed to be taken by any of the
-	 * NAPI code and this dummy netdev is supposed to be
-	 * only ever used for NAPI polls
-	 */
-	memset(dev, 0, sizeof(struct net_device));
-	init_dummy_netdev_core(dev);
-}
-EXPORT_SYMBOL_GPL(init_dummy_netdev);
-
 /**
  *	register_netdev	- register a network device
  *	@dev: device to register

net/mptcp/protocol.c

@@ -47,7 +47,7 @@ static void __mptcp_destroy_sock(struct sock *sk);
 static void mptcp_check_send_data_fin(struct sock *sk);
 
 DEFINE_PER_CPU(struct mptcp_delegated_action, mptcp_delegated_actions);
-static struct net_device mptcp_napi_dev;
+static struct net_device *mptcp_napi_dev;
 
 /* Returns end sequence number of the receiver's advertised window */
 static u64 mptcp_wnd_end(const struct mptcp_sock *msk)
@@ -4147,11 +4147,13 @@ void __init mptcp_proto_init(void)
 	if (percpu_counter_init(&mptcp_sockets_allocated, 0, GFP_KERNEL))
 		panic("Failed to allocate MPTCP pcpu counter\n");
 
-	init_dummy_netdev(&mptcp_napi_dev);
+	mptcp_napi_dev = alloc_netdev_dummy(0);
+	if (!mptcp_napi_dev)
+		panic("Failed to allocate MPTCP dummy netdev\n");
 	for_each_possible_cpu(cpu) {
 		delegated = per_cpu_ptr(&mptcp_delegated_actions, cpu);
 		INIT_LIST_HEAD(&delegated->head);
-		netif_napi_add_tx(&mptcp_napi_dev, &delegated->napi,
+		netif_napi_add_tx(mptcp_napi_dev, &delegated->napi,
 				  mptcp_napi_poll);
 		napi_enable(&delegated->napi);
 	}

net/xfrm/xfrm_input.c

@@ -48,7 +48,7 @@ static DEFINE_SPINLOCK(xfrm_input_afinfo_lock);
 static struct xfrm_input_afinfo const __rcu *xfrm_input_afinfo[2][AF_INET6 + 1];
 
 static struct gro_cells gro_cells;
-static struct net_device xfrm_napi_dev;
+static struct net_device *xfrm_napi_dev;
 
 static DEFINE_PER_CPU(struct xfrm_trans_tasklet, xfrm_trans_tasklet);
 
@@ -825,8 +825,11 @@ void __init xfrm_input_init(void)
 	int err;
 	int i;
 
-	init_dummy_netdev(&xfrm_napi_dev);
-	err = gro_cells_init(&gro_cells, &xfrm_napi_dev);
+	xfrm_napi_dev = alloc_netdev_dummy(0);
+	if (!xfrm_napi_dev)
+		panic("Failed to allocate XFRM dummy netdev\n");
+
+	err = gro_cells_init(&gro_cells, xfrm_napi_dev);
 	if (err)
 		gro_cells.cells = NULL;