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, 10 insertions, 7 deletions

diff --git a/net/tipc/discover.c b/net/tipc/discover.c
index 542fe34..3a8f211 100644
--- a/net/tipc/discover.c
+++ b/net/tipc/discover.c
@@ -46,8 +46,9 @@
 
 /**
  * struct tipc_link_req - information about an ongoing link setup request
- * @bearer: bearer issuing requests
+ * @bearer_id: identity of bearer issuing requests
  * @dest: destination address for request messages
+ * @domain: network domain to which links can be established
  * @num_nodes: number of nodes currently discovered (i.e. with an active link)
  * @lock: spinlock for controlling access to requests
  * @buf: request message to be (repeatedly) sent
@@ -55,8 +56,9 @@
  * @timer_intv: current interval between requests (in ms)
  */
 struct tipc_link_req {
-	struct tipc_bearer *bearer;
+	u32 bearer_id;
 	struct tipc_media_addr dest;
+	u32 domain;
 	int num_nodes;
 	spinlock_t lock;
 	struct sk_buff *buf;
@@ -241,7 +243,7 @@ void tipc_disc_rcv(struct sk_buff *buf, struct tipc_bearer *b_ptr)
 	if ((type == DSC_REQ_MSG) && !link_fully_up) {
 		rbuf = tipc_disc_init_msg(DSC_RESP_MSG, b_ptr);
 		if (rbuf) {
-			tipc_bearer_send(b_ptr, rbuf, &media_addr);
+			tipc_bearer_send(b_ptr->identity, rbuf, &media_addr);
 			kfree_skb(rbuf);
 		}
 	}
@@ -303,7 +305,7 @@ static void disc_timeout(struct tipc_link_req *req)
 	spin_lock_bh(&req->lock);
 
 	/* Stop searching if only desired node has been found */
-	if (tipc_node(req->bearer->domain) && req->num_nodes) {
+	if (tipc_node(req->domain) && req->num_nodes) {
 		req->timer_intv = TIPC_LINK_REQ_INACTIVE;
 		goto exit;
 	}
@@ -315,7 +317,7 @@ static void disc_timeout(struct tipc_link_req *req)
 	 * hold at fast polling rate if don't have any associated nodes,
 	 * otherwise hold at slow polling rate
 	 */
-	tipc_bearer_send(req->bearer, req->buf, &req->dest);
+	tipc_bearer_send(req->bearer_id, req->buf, &req->dest);
 
 
 	req->timer_intv *= 2;
@@ -354,14 +356,15 @@ int tipc_disc_create(struct tipc_bearer *b_ptr, struct tipc_media_addr *dest)
 	}
 
 	memcpy(&req->dest, dest, sizeof(*dest));
-	req->bearer = b_ptr;
+	req->bearer_id = b_ptr->identity;
+	req->domain = b_ptr->domain;
 	req->num_nodes = 0;
 	req->timer_intv = TIPC_LINK_REQ_INIT;
 	spin_lock_init(&req->lock);
 	k_init_timer(&req->timer, (Handler)disc_timeout, (unsigned long)req);
 	k_start_timer(&req->timer, req->timer_intv);
 	b_ptr->link_req = req;
-	tipc_bearer_send(req->bearer, req->buf, &req->dest);
+	tipc_bearer_send(req->bearer_id, req->buf, &req->dest);
 	return 0;
 }