netpoll: Remove dead packet receive code (CONFIG_NETPOLL_TRAP)

The netpoll packet receive code only becomes active if the netpoll
rx_skb_hook is implemented, and there is not a single implementation
of the netpoll rx_skb_hook in the kernel.

All of the out of tree implementations I have found all call
netpoll_poll which was removed from the kernel in 2011, so this
change should not add any additional breakage.

There are problems with the netpoll packet receive code.  __netpoll_rx
does not call dev_kfree_skb_irq or dev_kfree_skb_any in hard irq
context.  netpoll_neigh_reply leaks every skb it receives.  Reception
of packets does not work successfully on stacked devices (aka bonding,
team, bridge, and vlans).

Given that the netpoll packet receive code is buggy, there are no
out of tree users that will be merged soon, and the code has
not been used for in tree for a decade let's just remove it.

Reverting this commit can server as a starting point for anyone
who wants to resurrect netpoll packet reception support.
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/Kconfig

@@ -177,11 +177,6 @@ config NETCONSOLE_DYNAMIC
 config NETPOLL
 	def_bool NETCONSOLE
 
-config NETPOLL_TRAP
-	bool "Netpoll traffic trapping"
-	default n
-	depends on NETPOLL
-
 config NET_POLL_CONTROLLER
 	def_bool NETPOLL
 

include/linux/netdevice.h

@@ -1979,9 +1979,6 @@ struct net_device *__dev_get_by_index(struct net *net, int ifindex);
 struct net_device *dev_get_by_index_rcu(struct net *net, int ifindex);
 int netdev_get_name(struct net *net, char *name, int ifindex);
 int dev_restart(struct net_device *dev);
-#ifdef CONFIG_NETPOLL_TRAP
-int netpoll_trap(void);
-#endif
 int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb);
 
 static inline unsigned int skb_gro_offset(const struct sk_buff *skb)
@@ -2186,12 +2183,6 @@ static inline void netif_tx_start_all_queues(struct net_device *dev)
 
 static inline void netif_tx_wake_queue(struct netdev_queue *dev_queue)
 {
-#ifdef CONFIG_NETPOLL_TRAP
-	if (netpoll_trap()) {
-		netif_tx_start_queue(dev_queue);
-		return;
-	}
-#endif
 	if (test_and_clear_bit(__QUEUE_STATE_DRV_XOFF, &dev_queue->state))
 		__netif_schedule(dev_queue->qdisc);
 }
@@ -2435,10 +2426,6 @@ static inline void netif_start_subqueue(struct net_device *dev, u16 queue_index)
 static inline void netif_stop_subqueue(struct net_device *dev, u16 queue_index)
 {
 	struct netdev_queue *txq = netdev_get_tx_queue(dev, queue_index);
-#ifdef CONFIG_NETPOLL_TRAP
-	if (netpoll_trap())
-		return;
-#endif
 	netif_tx_stop_queue(txq);
 }
 
@@ -2473,10 +2460,6 @@ static inline bool netif_subqueue_stopped(const struct net_device *dev,
 static inline void netif_wake_subqueue(struct net_device *dev, u16 queue_index)
 {
 	struct netdev_queue *txq = netdev_get_tx_queue(dev, queue_index);
-#ifdef CONFIG_NETPOLL_TRAP
-	if (netpoll_trap())
-		return;
-#endif
 	if (test_and_clear_bit(__QUEUE_STATE_DRV_XOFF, &txq->state))
 		__netif_schedule(txq->qdisc);
 }

include/linux/netpoll.h

@@ -31,12 +31,6 @@ struct netpoll {
 	u8 remote_mac[ETH_ALEN];
 
 	struct work_struct cleanup_work;
-
-#ifdef CONFIG_NETPOLL_TRAP
-	void (*rx_skb_hook)(struct netpoll *np, int source, struct sk_buff *skb,
-			    int offset, int len);
-	struct list_head rx; /* rx_np list element */
-#endif
 };
 
 struct netpoll_info {
@@ -50,12 +44,6 @@ struct netpoll_info {
 
 	struct netpoll *netpoll;
 	struct rcu_head rcu;
-
-#ifdef CONFIG_NETPOLL_TRAP
-	spinlock_t rx_lock;
-	struct list_head rx_np; /* netpolls that registered an rx_skb_hook */
-	struct sk_buff_head neigh_tx; /* list of neigh requests to reply to */
-#endif
 };
 
 #ifdef CONFIG_NETPOLL
@@ -84,78 +72,6 @@ static inline void netpoll_send_skb(struct netpoll *np, struct sk_buff *skb)
 	local_irq_restore(flags);
 }
 
-#ifdef CONFIG_NETPOLL_TRAP
-int netpoll_trap(void);
-void netpoll_set_trap(int trap);
-int __netpoll_rx(struct sk_buff *skb, struct netpoll_info *npinfo);
-static inline bool netpoll_rx_processing(struct netpoll_info *npinfo)
-{
-	return !list_empty(&npinfo->rx_np);
-}
-
-static inline bool netpoll_rx_on(struct sk_buff *skb)
-{
-	struct netpoll_info *npinfo = rcu_dereference_bh(skb->dev->npinfo);
-
-	return npinfo && netpoll_rx_processing(npinfo);
-}
-
-static inline bool netpoll_rx(struct sk_buff *skb)
-{
-	struct netpoll_info *npinfo;
-	unsigned long flags;
-	bool ret = false;
-
-	local_irq_save(flags);
-
-	if (!netpoll_rx_on(skb))
-		goto out;
-
-	npinfo = rcu_dereference_bh(skb->dev->npinfo);
-	spin_lock(&npinfo->rx_lock);
-	/* check rx_processing again with the lock held */
-	if (netpoll_rx_processing(npinfo) && __netpoll_rx(skb, npinfo))
-		ret = true;
-	spin_unlock(&npinfo->rx_lock);
-
-out:
-	local_irq_restore(flags);
-	return ret;
-}
-
-static inline int netpoll_receive_skb(struct sk_buff *skb)
-{
-	if (!list_empty(&skb->dev->napi_list))
-		return netpoll_rx(skb);
-	return 0;
-}
-
-#else
-static inline int netpoll_trap(void)
-{
-	return 0;
-}
-static inline void netpoll_set_trap(int trap)
-{
-}
-static inline bool netpoll_rx_processing(struct netpoll_info *npinfo)
-{
-	return false;
-}
-static inline bool netpoll_rx(struct sk_buff *skb)
-{
-	return false;
-}
-static inline bool netpoll_rx_on(struct sk_buff *skb)
-{
-	return false;
-}
-static inline int netpoll_receive_skb(struct sk_buff *skb)
-{
-	return 0;
-}
-#endif
-
 #ifdef CONFIG_NETPOLL
 static inline void *netpoll_poll_lock(struct napi_struct *napi)
 {

net/core/dev.c

@@ -3231,10 +3231,6 @@ static int netif_rx_internal(struct sk_buff *skb)
 {
 	int ret;
 
-	/* if netpoll wants it, pretend we never saw it */
-	if (netpoll_rx(skb))
-		return NET_RX_DROP;
-
 	net_timestamp_check(netdev_tstamp_prequeue, skb);
 
 	trace_netif_rx(skb);
@@ -3520,10 +3516,6 @@ static int __netif_receive_skb_core(struct sk_buff *skb, bool pfmemalloc)
 
 	trace_netif_receive_skb(skb);
 
-	/* if we've gotten here through NAPI, check netpoll */
-	if (netpoll_receive_skb(skb))
-		goto out;
-
 	orig_dev = skb->dev;
 
 	skb_reset_network_header(skb);
@@ -3650,7 +3642,6 @@ static int __netif_receive_skb_core(struct sk_buff *skb, bool pfmemalloc)
 
 unlock:
 	rcu_read_unlock();
-out:
 	return ret;
 }
 
@@ -3875,7 +3866,7 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 	int same_flow;
 	enum gro_result ret;
 
-	if (!(skb->dev->features & NETIF_F_GRO) || netpoll_rx_on(skb))
+	if (!(skb->dev->features & NETIF_F_GRO))
 		goto normal;
 
 	if (skb_is_gso(skb) || skb_has_frag_list(skb))