commit 37cb0620073cb64101d9307931c135c70b2e3f04
author Ying Xue <ying.xue@windriver.com> Tue Dec 10 20:45:41 2013 -0800
committer David S. Miller <davem@davemloft.net> Wed Dec 11 00:17:42 2013 -0500
tree 302cb1bf079ddf1b09dd79cb965d55566d2b75a5
parent ef72a7e02a28adfd9d5d0d1de81c0b75f3823aa5

tipc: remove TIPC usage of field af_packet_priv in struct net_device

TIPC is currently using the field 'af_packet_priv' in struct net_device
as a handle to find the bearer instance associated to the given network
device. But, by doing so it is blocking other networking cleanups, such
as the one discussed here:

http://patchwork.ozlabs.org/patch/178044/

This commit removes this usage from TIPC. Instead, we introduce a new
field, 'tipc_ptr', to the net_device structure, to serve this purpose.
When TIPC bearer is enabled, the bearer object is associated to
'tipc_ptr'. When a TIPC packet arrives in the recv_msg() upcall
from a networking device, the bearer object can now be obtained from
'tipc_ptr'. When a bearer is disabled, the bearer object is detached
from its underlying network device by setting 'tipc_ptr' to NULL.

Additionally, an RCU lock is used to protect the new pointer.
Henceforth, the existing tipc_net_lock is used in write mode to
serialize write accesses to this pointer, while the new RCU lock is
applied on the read side to ensure that the pointer is 100% valid
within its wrapped area for all readers.

Signed-off-by: Ying Xue <ying.xue@windriver.com>
Cc: Patrick McHardy <kaber@trash.net>
Reviewed-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/eth_media.c

diff --git a/net/tipc/eth_media.c b/net/tipc/eth_media.c
index 37fb145..c5f685d 100644
--- a/net/tipc/eth_media.c
+++ b/net/tipc/eth_media.c
@@ -63,6 +63,9 @@
 
 static int recv_notification(struct notifier_block *nb, unsigned long evt,
 			     void *dv);
+static int recv_msg(struct sk_buff *buf, struct net_device *dev,
+		    struct packet_type *pt, struct net_device *orig_dev);
+
 /*
  * Network device notifier info
  */
@@ -71,6 +74,11 @@
 	.priority	= 0
 };
 
+static struct packet_type tipc_packet_type __read_mostly = {
+	.type = __constant_htons(ETH_P_TIPC),
+	.func = recv_msg,
+};
+
 /**
  * eth_media_addr_set - initialize Ethernet media address structure
  *
@@ -128,20 +136,25 @@
 static int recv_msg(struct sk_buff *buf, struct net_device *dev,
 		    struct packet_type *pt, struct net_device *orig_dev)
 {
-	struct eth_media *eb_ptr = (struct eth_media *)pt->af_packet_priv;
+	struct tipc_bearer *b_ptr;
 
 	if (!net_eq(dev_net(dev), &init_net)) {
 		kfree_skb(buf);
 		return NET_RX_DROP;
 	}
 
-	if (likely(eb_ptr->bearer)) {
+	rcu_read_lock();
+	b_ptr = rcu_dereference(dev->tipc_ptr);
+	if (likely(b_ptr)) {
 		if (likely(buf->pkt_type <= PACKET_BROADCAST)) {
 			buf->next = NULL;
-			tipc_recv_msg(buf, eb_ptr->bearer);
+			tipc_recv_msg(buf, b_ptr);
+			rcu_read_unlock();
 			return NET_RX_SUCCESS;
 		}
 	}
+	rcu_read_unlock();
+
 	kfree_skb(buf);
 	return NET_RX_DROP;
 }
@@ -151,10 +164,7 @@
  */
 static void setup_media(struct work_struct *work)
 {
-	struct eth_media *eb_ptr =
-		container_of(work, struct eth_media, setup);
-
-	dev_add_pack(&eb_ptr->tipc_packet_type);
+	dev_add_pack(&tipc_packet_type);
 }
 
 /**
@@ -183,15 +193,11 @@
 
 	/* Create Ethernet bearer for device */
 	eb_ptr->dev = dev;
-	eb_ptr->tipc_packet_type.type = htons(ETH_P_TIPC);
-	eb_ptr->tipc_packet_type.dev = dev;
-	eb_ptr->tipc_packet_type.func = recv_msg;
-	eb_ptr->tipc_packet_type.af_packet_priv = eb_ptr;
-	INIT_LIST_HEAD(&(eb_ptr->tipc_packet_type.list));
 	INIT_WORK(&eb_ptr->setup, setup_media);
 	schedule_work(&eb_ptr->setup);
 
 	/* Associate TIPC bearer with Ethernet bearer */
+	tb_ptr->dev = dev;
 	eb_ptr->bearer = tb_ptr;
 	tb_ptr->usr_handle = (void *)eb_ptr;
 	memset(tb_ptr->bcast_addr.value, 0, sizeof(tb_ptr->bcast_addr.value));
@@ -200,6 +206,7 @@
 	tb_ptr->bcast_addr.broadcast = 1;
 	tb_ptr->mtu = dev->mtu;
 	eth_media_addr_set(tb_ptr, &tb_ptr->addr, (char *)dev->dev_addr);
+	rcu_assign_pointer(dev->tipc_ptr, tb_ptr);
 	return 0;
 }
 
@@ -213,7 +220,7 @@
 	struct eth_media *eb_ptr =
 		container_of(work, struct eth_media, cleanup);
 
-	dev_remove_pack(&eb_ptr->tipc_packet_type);
+	dev_remove_pack(&tipc_packet_type);
 	dev_put(eb_ptr->dev);
 	eb_ptr->dev = NULL;
 }
@@ -232,6 +239,7 @@
 	eb_ptr->bearer = NULL;
 	INIT_WORK(&eb_ptr->cleanup, cleanup_media);
 	schedule_work(&eb_ptr->cleanup);
+	RCU_INIT_POINTER(tb_ptr->dev->tipc_ptr, NULL);
 }
 
 /**
@@ -243,21 +251,20 @@
 static int recv_notification(struct notifier_block *nb, unsigned long evt,
 			     void *ptr)
 {
+	struct tipc_bearer *b_ptr;
 	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
-	struct eth_media *eb_ptr = &eth_media_array[0];
-	struct eth_media *stop = &eth_media_array[MAX_ETH_MEDIA];
 
 	if (!net_eq(dev_net(dev), &init_net))
 		return NOTIFY_DONE;
 
-	while ((eb_ptr->dev != dev)) {
-		if (++eb_ptr == stop)
-			return NOTIFY_DONE;	/* couldn't find device */
-	}
-	if (!eb_ptr->bearer)
+	rcu_read_lock();
+	b_ptr = rcu_dereference(dev->tipc_ptr);
+	if (!b_ptr) {
+		rcu_read_unlock();
 		return NOTIFY_DONE;		/* bearer had been disabled */
+	}
 
-	eb_ptr->bearer->mtu = dev->mtu;
+	b_ptr->mtu = dev->mtu;
 
 	switch (evt) {
 	case NETDEV_CHANGE:
@@ -266,13 +273,15 @@
 	case NETDEV_DOWN:
 	case NETDEV_CHANGEMTU:
 	case NETDEV_CHANGEADDR:
-		tipc_reset_bearer(eb_ptr->bearer);
+		tipc_reset_bearer(b_ptr);
 		break;
 	case NETDEV_UNREGISTER:
 	case NETDEV_CHANGENAME:
-		tipc_disable_bearer(eb_ptr->bearer->name);
+		tipc_disable_bearer(b_ptr->name);
 		break;
 	}
+	rcu_read_unlock();
+
 	return NOTIFY_OK;
 }