tipc: decouple the relationship between bearer and link

Currently on both paths of message transmission and reception, the
read lock of tipc_net_lock must be held before bearer is accessed,
while the write lock of tipc_net_lock has to be taken before bearer
is configured. Although it can ensure that bearer is always valid on
the two data paths, link and bearer is closely bound together.

So as the part of effort of removing tipc_net_lock, the locking
policy of bearer protection will be adjusted as below: on the two
data paths, RCU is used, and on the configuration path of bearer,
RTNL lock is applied.

Now RCU just covers the path of message reception. To make it possible
to protect the path of message transmission with RCU, link should not
use its stored bearer pointer to access bearer, but it should use the
bearer identity of its attached bearer as index to get bearer instance
from bearer_list array, which can help us decouple the relationship
between bearer and link. As a result, bearer on the path of message
transmission can be safely protected by RCU when we access bearer_list
array within RCU lock protection.

Signed-off-by: Ying Xue <ying.xue@windriver.com>
Reviewed-by: Jon Maloy <jon.maloy@ericsson.com>
Reviewed-by: Erik Hugne <erik.hugne@ericsson.com>
Tested-by: Erik Hugne <erik.hugne@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 33 insertions, 16 deletions

diff --git a/net/tipc/link.c b/net/tipc/link.c
index c5190ab75290..229d478494b9 100644
--- a/net/tipc/link.c
+++ b/net/tipc/link.c
@@ -101,9 +101,18 @@ static unsigned int align(unsigned int i)
 
 static void link_init_max_pkt(struct tipc_link *l_ptr)
 {
+	struct tipc_bearer *b_ptr;
 	u32 max_pkt;
 
-	max_pkt = (l_ptr->b_ptr->mtu & ~3);
+	rcu_read_lock();
+	b_ptr = rcu_dereference_rtnl(bearer_list[l_ptr->bearer_id]);
+	if (!b_ptr) {
+		rcu_read_unlock();
+		return;
+	}
+	max_pkt = (b_ptr->mtu & ~3);
+	rcu_read_unlock();
+
 	if (max_pkt > MAX_MSG_SIZE)
 		max_pkt = MAX_MSG_SIZE;
 
@@ -248,7 +257,7 @@ struct tipc_link *tipc_link_create(struct tipc_node *n_ptr,
 	l_ptr->owner = n_ptr;
 	l_ptr->checkpoint = 1;
 	l_ptr->peer_session = INVALID_SESSION;
-	l_ptr->b_ptr = b_ptr;
+	l_ptr->bearer_id = b_ptr->identity;
 	link_set_supervision_props(l_ptr, b_ptr->tolerance);
 	l_ptr->state = RESET_UNKNOWN;
 
@@ -263,6 +272,7 @@ struct tipc_link *tipc_link_create(struct tipc_node *n_ptr,
 	l_ptr->priority = b_ptr->priority;
 	tipc_link_set_queue_limits(l_ptr, b_ptr->window);
 
+	l_ptr->net_plane = b_ptr->net_plane;
 	link_init_max_pkt(l_ptr);
 
 	l_ptr->next_out_no = 1;
@@ -426,7 +436,7 @@ void tipc_link_reset(struct tipc_link *l_ptr)
 		return;
 
 	tipc_node_link_down(l_ptr->owner, l_ptr);
-	tipc_bearer_remove_dest(l_ptr->b_ptr, l_ptr->addr);
+	tipc_bearer_remove_dest(l_ptr->bearer_id, l_ptr->addr);
 
 	if (was_active_link && tipc_node_active_links(l_ptr->owner)) {
 		l_ptr->reset_checkpoint = checkpoint;
@@ -477,7 +487,7 @@ static void link_activate(struct tipc_link *l_ptr)
 {
 	l_ptr->next_in_no = l_ptr->stats.recv_info = 1;
 	tipc_node_link_up(l_ptr->owner, l_ptr);
-	tipc_bearer_add_dest(l_ptr->b_ptr, l_ptr->addr);
+	tipc_bearer_add_dest(l_ptr->bearer_id, l_ptr->addr);
 }
 
 /**
@@ -777,7 +787,7 @@ int __tipc_link_xmit(struct tipc_link *l_ptr, struct sk_buff *buf)
 	if (likely(!link_congested(l_ptr))) {
 		link_add_to_outqueue(l_ptr, buf, msg);
 
-		tipc_bearer_send(l_ptr->b_ptr, buf, &l_ptr->media_addr);
+		tipc_bearer_send(l_ptr->bearer_id, buf, &l_ptr->media_addr);
 		l_ptr->unacked_window = 0;
 		return dsz;
 	}
@@ -941,7 +951,7 @@ static int tipc_link_xmit_fast(struct tipc_link *l_ptr, struct sk_buff *buf,
 	if (likely(!link_congested(l_ptr))) {
 		if (likely(msg_size(msg) <= l_ptr->max_pkt)) {
 			link_add_to_outqueue(l_ptr, buf, msg);
-			tipc_bearer_send(l_ptr->b_ptr, buf,
+			tipc_bearer_send(l_ptr->bearer_id, buf,
 					 &l_ptr->media_addr);
 			l_ptr->unacked_window = 0;
 			return res;
@@ -1204,7 +1214,7 @@ static u32 tipc_link_push_packet(struct tipc_link *l_ptr)
 	if (r_q_size && buf) {
 		msg_set_ack(buf_msg(buf), mod(l_ptr->next_in_no - 1));
 		msg_set_bcast_ack(buf_msg(buf), l_ptr->owner->bclink.last_in);
-		tipc_bearer_send(l_ptr->b_ptr, buf, &l_ptr->media_addr);
+		tipc_bearer_send(l_ptr->bearer_id, buf, &l_ptr->media_addr);
 		l_ptr->retransm_queue_head = mod(++r_q_head);
 		l_ptr->retransm_queue_size = --r_q_size;
 		l_ptr->stats.retransmitted++;
@@ -1216,7 +1226,7 @@ static u32 tipc_link_push_packet(struct tipc_link *l_ptr)
 	if (buf) {
 		msg_set_ack(buf_msg(buf), mod(l_ptr->next_in_no - 1));
 		msg_set_bcast_ack(buf_msg(buf), l_ptr->owner->bclink.last_in);
-		tipc_bearer_send(l_ptr->b_ptr, buf, &l_ptr->media_addr);
+		tipc_bearer_send(l_ptr->bearer_id, buf, &l_ptr->media_addr);
 		l_ptr->unacked_window = 0;
 		kfree_skb(buf);
 		l_ptr->proto_msg_queue = NULL;
@@ -1233,7 +1243,8 @@ static u32 tipc_link_push_packet(struct tipc_link *l_ptr)
 		if (mod(next - first) < l_ptr->queue_limit[0]) {
 			msg_set_ack(msg, mod(l_ptr->next_in_no - 1));
 			msg_set_bcast_ack(msg, l_ptr->owner->bclink.last_in);
-			tipc_bearer_send(l_ptr->b_ptr, buf, &l_ptr->media_addr);
+			tipc_bearer_send(l_ptr->bearer_id, buf,
+					 &l_ptr->media_addr);
 			if (msg_user(msg) == MSG_BUNDLER)
 				msg_set_type(msg, CLOSED_MSG);
 			l_ptr->next_out = buf->next;
@@ -1352,7 +1363,7 @@ void tipc_link_retransmit(struct tipc_link *l_ptr, struct sk_buff *buf,
 		msg = buf_msg(buf);
 		msg_set_ack(msg, mod(l_ptr->next_in_no - 1));
 		msg_set_bcast_ack(msg, l_ptr->owner->bclink.last_in);
-		tipc_bearer_send(l_ptr->b_ptr, buf, &l_ptr->media_addr);
+		tipc_bearer_send(l_ptr->bearer_id, buf, &l_ptr->media_addr);
 		buf = buf->next;
 		retransmits--;
 		l_ptr->stats.retransmitted++;
@@ -1440,7 +1451,7 @@ static int link_recv_buf_validate(struct sk_buff *buf)
 /**
  * tipc_rcv - process TIPC packets/messages arriving from off-node
  * @head: pointer to message buffer chain
- * @tb_ptr: pointer to bearer message arrived on
+ * @b_ptr: pointer to bearer message arrived on
  *
  * Invoked with no locks held.  Bearer pointer must point to a valid bearer
  * structure (i.e. cannot be NULL), but bearer can be inactive.
@@ -1752,7 +1763,7 @@ void tipc_link_proto_xmit(struct tipc_link *l_ptr, u32 msg_typ, int probe_msg,
 
 	/* Create protocol message with "out-of-sequence" sequence number */
 	msg_set_type(msg, msg_typ);
-	msg_set_net_plane(msg, l_ptr->b_ptr->net_plane);
+	msg_set_net_plane(msg, l_ptr->net_plane);
 	msg_set_bcast_ack(msg, l_ptr->owner->bclink.last_in);
 	msg_set_last_bcast(msg, tipc_bclink_get_last_sent());
 
@@ -1818,7 +1829,7 @@ void tipc_link_proto_xmit(struct tipc_link *l_ptr, u32 msg_typ, int probe_msg,
 	skb_copy_to_linear_data(buf, msg, sizeof(l_ptr->proto_msg));
 	buf->priority = TC_PRIO_CONTROL;
 
-	tipc_bearer_send(l_ptr->b_ptr, buf, &l_ptr->media_addr);
+	tipc_bearer_send(l_ptr->bearer_id, buf, &l_ptr->media_addr);
 	l_ptr->unacked_window = 0;
 	kfree_skb(buf);
 }
@@ -1843,9 +1854,9 @@ static void tipc_link_proto_rcv(struct tipc_link *l_ptr, struct sk_buff *buf)
 	/* record unnumbered packet arrival (force mismatch on next timeout) */
 	l_ptr->checkpoint--;
 
-	if (l_ptr->b_ptr->net_plane != msg_net_plane(msg))
+	if (l_ptr->net_plane != msg_net_plane(msg))
 		if (tipc_own_addr > msg_prevnode(msg))
-			l_ptr->b_ptr->net_plane = msg_net_plane(msg);
+			l_ptr->net_plane = msg_net_plane(msg);
 
 	switch (msg_type(msg)) {
 
@@ -2793,7 +2804,13 @@ u32 tipc_link_get_max_pkt(u32 dest, u32 selector)
 
 static void link_print(struct tipc_link *l_ptr, const char *str)
 {
-	pr_info("%s Link %x<%s>:", str, l_ptr->addr, l_ptr->b_ptr->name);
+	struct tipc_bearer *b_ptr;
+
+	rcu_read_lock();
+	b_ptr = rcu_dereference_rtnl(bearer_list[l_ptr->bearer_id]);
+	if (b_ptr)
+		pr_info("%s Link %x<%s>:", str, l_ptr->addr, b_ptr->name);
+	rcu_read_unlock();
 
 	if (link_working_unknown(l_ptr))
 		pr_cont(":WU\n");