[net-next,RFC] net: x25: Queue received packets in the drivers instead of per-CPU queues

diff --git a/Documentation/networking/x25-iface.rst b/Documentation/networking/x25-iface.rst
index df401891dce6..f34e9ec64937 100644
--- a/Documentation/networking/x25-iface.rst
+++ b/Documentation/networking/x25-iface.rst
@@ -70,60 +70,13 @@  First Byte = 0x03 (X25_IFACE_PARAMS)
 LAPB parameters. To be defined.
 
 
+Requirements for the device driver
+----------------------------------
 
-Possible Problems
-=================
-
-(Henner Eisen, 2000-10-28)
-
-The X.25 packet layer protocol depends on a reliable datalink service.
-The LAPB protocol provides such reliable service. But this reliability
-is not preserved by the Linux network device driver interface:
-
-- With Linux 2.4.x (and above) SMP kernels, packet ordering is not
-  preserved. Even if a device driver calls netif_rx(skb1) and later
-  netif_rx(skb2), skb2 might be delivered to the network layer
-  earlier that skb1.
-- Data passed upstream by means of netif_rx() might be dropped by the
-  kernel if the backlog queue is congested.
-
-The X.25 packet layer protocol will detect this and reset the virtual
-call in question. But many upper layer protocols are not designed to
-handle such N-Reset events gracefully. And frequent N-Reset events
-will always degrade performance.
-
-Thus, driver authors should make netif_rx() as reliable as possible:
-
-SMP re-ordering will not occur if the driver's interrupt handler is
-always executed on the same CPU. Thus,
-
-- Driver authors should use irq affinity for the interrupt handler.
-
-The probability of packet loss due to backlog congestion can be
-reduced by the following measures or a combination thereof:
-
-(1) Drivers for kernel versions 2.4.x and above should always check the
-    return value of netif_rx(). If it returns NET_RX_DROP, the
-    driver's LAPB protocol must not confirm reception of the frame
-    to the peer.
-    This will reliably suppress packet loss. The LAPB protocol will
-    automatically cause the peer to re-transmit the dropped packet
-    later.
-    The lapb module interface was modified to support this. Its
-    data_indication() method should now transparently pass the
-    netif_rx() return value to the (lapb module) caller.
-(2) Drivers for kernel versions 2.2.x should always check the global
-    variable netdev_dropping when a new frame is received. The driver
-    should only call netif_rx() if netdev_dropping is zero. Otherwise
-    the driver should not confirm delivery of the frame and drop it.
-    Alternatively, the driver can queue the frame internally and call
-    netif_rx() later when netif_dropping is 0 again. In that case, delivery
-    confirmation should also be deferred such that the internal queue
-    cannot grow to much.
-    This will not reliably avoid packet loss, but the probability
-    of packet loss in netif_rx() path will be significantly reduced.
-(3) Additionally, driver authors might consider to support
-    CONFIG_NET_HW_FLOWCONTROL. This allows the driver to be woken up
-    when a previously congested backlog queue becomes empty again.
-    The driver could uses this for flow-controlling the peer by means
-    of the LAPB protocol's flow-control service.
+Packets should not be reordered or dropped when delivering between the
+Packet Layer and the device driver.
+
+To avoid packets from being reordered or dropped when delivering from
+the device driver to the Packet Layer, the device driver should not
+call "netif_rx" to deliver the received packets. Instead, it should
+call "netif_receive_skb_core" from softirq context to deliver them.
diff --git a/drivers/net/wan/hdlc_x25.c b/drivers/net/wan/hdlc_x25.c
index 4aaa6388b9ee..28e9cb2c5f1e 100644
--- a/drivers/net/wan/hdlc_x25.c
+++ b/drivers/net/wan/hdlc_x25.c
@@ -23,6 +23,8 @@ 
 
 struct x25_state {
 	x25_hdlc_proto settings;
+	struct sk_buff_head rx_queue;
+	struct tasklet_struct rx_tasklet;
 };
 
 static int x25_ioctl(struct net_device *dev, struct ifreq *ifr);
@@ -32,10 +34,22 @@  static struct x25_state *state(hdlc_device *hdlc)
 	return hdlc->state;
 }
 
+static void x25_rx_queue_kick(struct tasklet_struct *t)
+{
+	struct x25_state *x25st = from_tasklet(x25st, t, rx_tasklet);
+	struct sk_buff *skb = skb_dequeue(&x25st->rx_queue);
+
+	while (skb) {
+		netif_receive_skb_core(skb);
+		skb = skb_dequeue(&x25st->rx_queue);
+	}
+}
+
 /* These functions are callbacks called by LAPB layer */
 
 static void x25_connect_disconnect(struct net_device *dev, int reason, int code)
 {
+	struct x25_state *x25st = state(dev_to_hdlc(dev));
 	struct sk_buff *skb;
 	unsigned char *ptr;
 
@@ -48,7 +62,9 @@  static void x25_connect_disconnect(struct net_device *dev, int reason, int code)
 	*ptr = code;
 
 	skb->protocol = x25_type_trans(skb, dev);
-	netif_rx(skb);
+
+	skb_queue_tail(&x25st->rx_queue, skb);
+	tasklet_schedule(&x25st->rx_tasklet);
 }
 
 
@@ -69,6 +85,7 @@  static void x25_disconnected(struct net_device *dev, int reason)
 
 static int x25_data_indication(struct net_device *dev, struct sk_buff *skb)
 {
+	struct x25_state *x25st = state(dev_to_hdlc(dev));
 	unsigned char *ptr;
 
 	if (skb_cow(skb, 1)) {
@@ -82,7 +99,10 @@  static int x25_data_indication(struct net_device *dev, struct sk_buff *skb)
 	*ptr = X25_IFACE_DATA;
 
 	skb->protocol = x25_type_trans(skb, dev);
-	return netif_rx(skb);
+
+	skb_queue_tail(&x25st->rx_queue, skb);
+	tasklet_schedule(&x25st->rx_tasklet);
+	return NET_RX_SUCCESS;
 }
 
 
@@ -197,7 +217,10 @@  static int x25_open(struct net_device *dev)
 
 static void x25_close(struct net_device *dev)
 {
+	struct x25_state *x25st = state(dev_to_hdlc(dev));
+
 	lapb_unregister(dev);
+	tasklet_kill(&x25st->rx_tasklet);
 }
 
 
@@ -298,6 +321,8 @@  static int x25_ioctl(struct net_device *dev, struct ifreq *ifr)
 			return result;
 
 		memcpy(&state(hdlc)->settings, &new_settings, size);
+		skb_queue_head_init(&state(hdlc)->rx_queue);
+		tasklet_setup(&state(hdlc)->rx_tasklet, x25_rx_queue_kick);
 
 		/* There's no header_ops so hard_header_len should be 0. */
 		dev->hard_header_len = 0;
diff --git a/drivers/net/wan/lapbether.c b/drivers/net/wan/lapbether.c
index 605fe555e157..c85b2a1c8067 100644
--- a/drivers/net/wan/lapbether.c
+++ b/drivers/net/wan/lapbether.c
@@ -51,6 +51,8 @@  struct lapbethdev {
 	struct list_head	node;
 	struct net_device	*ethdev;	/* link to ethernet device */
 	struct net_device	*axdev;		/* lapbeth device (lapb#) */
+	struct sk_buff_head	rx_queue;
+	struct napi_struct	napi;
 };
 
 static LIST_HEAD(lapbeth_devices);
@@ -81,6 +83,25 @@  static __inline__ int dev_is_ethdev(struct net_device *dev)
 
 /* ------------------------------------------------------------------------ */
 
+static int lapbeth_napi_poll(struct napi_struct *napi, int budget)
+{
+	struct lapbethdev *lapbeth = container_of(napi, struct lapbethdev, napi);
+	struct sk_buff *skb;
+	int processed = 0;
+
+	for (; processed < budget; ++processed) {
+		skb = skb_dequeue(&lapbeth->rx_queue);
+		if (!skb)
+			break;
+		netif_receive_skb_core(skb);
+	}
+
+	if (processed < budget)
+		napi_complete(napi);
+
+	return processed;
+}
+
 /*
  *	Receive a LAPB frame via an ethernet interface.
  */
@@ -129,6 +150,7 @@  static int lapbeth_rcv(struct sk_buff *skb, struct net_device *dev, struct packe
 
 static int lapbeth_data_indication(struct net_device *dev, struct sk_buff *skb)
 {
+	struct lapbethdev *lapbeth = netdev_priv(dev);
 	unsigned char *ptr;
 
 	if (skb_cow(skb, 1)) {
@@ -142,7 +164,10 @@  static int lapbeth_data_indication(struct net_device *dev, struct sk_buff *skb)
 	*ptr = X25_IFACE_DATA;
 
 	skb->protocol = x25_type_trans(skb, dev);
-	return netif_rx(skb);
+
+	skb_queue_tail(&lapbeth->rx_queue, skb);
+	napi_schedule(&lapbeth->napi);
+	return NET_RX_SUCCESS;
 }
 
 /*
@@ -228,6 +253,7 @@  static void lapbeth_data_transmit(struct net_device *ndev, struct sk_buff *skb)
 
 static void lapbeth_connected(struct net_device *dev, int reason)
 {
+	struct lapbethdev *lapbeth = netdev_priv(dev);
 	unsigned char *ptr;
 	struct sk_buff *skb = dev_alloc_skb(1);
 
@@ -240,11 +266,14 @@  static void lapbeth_connected(struct net_device *dev, int reason)
 	*ptr = X25_IFACE_CONNECT;
 
 	skb->protocol = x25_type_trans(skb, dev);
-	netif_rx(skb);
+
+	skb_queue_tail(&lapbeth->rx_queue, skb);
+	napi_schedule(&lapbeth->napi);
 }
 
 static void lapbeth_disconnected(struct net_device *dev, int reason)
 {
+	struct lapbethdev *lapbeth = netdev_priv(dev);
 	unsigned char *ptr;
 	struct sk_buff *skb = dev_alloc_skb(1);
 
@@ -257,7 +286,9 @@  static void lapbeth_disconnected(struct net_device *dev, int reason)
 	*ptr = X25_IFACE_DISCONNECT;
 
 	skb->protocol = x25_type_trans(skb, dev);
-	netif_rx(skb);
+
+	skb_queue_tail(&lapbeth->rx_queue, skb);
+	napi_schedule(&lapbeth->napi);
 }
 
 /*
@@ -285,8 +316,11 @@  static const struct lapb_register_struct lapbeth_callbacks = {
  */
 static int lapbeth_open(struct net_device *dev)
 {
+	struct lapbethdev *lapbeth = netdev_priv(dev);
 	int err;
 
+	napi_enable(&lapbeth->napi);
+
 	if ((err = lapb_register(dev, &lapbeth_callbacks)) != LAPB_OK) {
 		pr_err("lapb_register error: %d\n", err);
 		return -ENODEV;
@@ -298,6 +332,7 @@  static int lapbeth_open(struct net_device *dev)
 
 static int lapbeth_close(struct net_device *dev)
 {
+	struct lapbethdev *lapbeth = netdev_priv(dev);
 	int err;
 
 	netif_stop_queue(dev);
@@ -305,6 +340,8 @@  static int lapbeth_close(struct net_device *dev)
 	if ((err = lapb_unregister(dev)) != LAPB_OK)
 		pr_err("lapb_unregister error: %d\n", err);
 
+	napi_disable(&lapbeth->napi);
+
 	return 0;
 }
 
@@ -359,6 +396,9 @@  static int lapbeth_new_device(struct net_device *dev)
 	dev_hold(dev);
 	lapbeth->ethdev = dev;
 
+	skb_queue_head_init(&lapbeth->rx_queue);
+	netif_napi_add(ndev, &lapbeth->napi, lapbeth_napi_poll, 16);
+
 	rc = -EIO;
 	if (register_netdevice(ndev))
 		goto fail;