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, 30 insertions, 10 deletions

diff --git a/net/tipc/bearer.c b/net/tipc/bearer.c
index 65b17639e43d..e0625e9e2c72 100644
--- a/net/tipc/bearer.c
+++ b/net/tipc/bearer.c
@@ -215,18 +215,32 @@ struct sk_buff *tipc_bearer_get_names(void)
         return buf;
 }
 
-void tipc_bearer_add_dest(struct tipc_bearer *b_ptr, u32 dest)
+void tipc_bearer_add_dest(u32 bearer_id, u32 dest)
 {
-        tipc_nmap_add(&b_ptr->nodes, dest);
-        tipc_bcbearer_sort();
-        tipc_disc_add_dest(b_ptr->link_req);
+        struct tipc_bearer *b_ptr;
+
+        rcu_read_lock();
+        b_ptr = rcu_dereference_rtnl(bearer_list[bearer_id]);
+        if (b_ptr) {
+                tipc_nmap_add(&b_ptr->nodes, dest);
+                tipc_bcbearer_sort();
+                tipc_disc_add_dest(b_ptr->link_req);
+        }
+        rcu_read_unlock();
 }
 
-void tipc_bearer_remove_dest(struct tipc_bearer *b_ptr, u32 dest)
+void tipc_bearer_remove_dest(u32 bearer_id, u32 dest)
 {
-        tipc_nmap_remove(&b_ptr->nodes, dest);
-        tipc_bcbearer_sort();
-        tipc_disc_remove_dest(b_ptr->link_req);
+        struct tipc_bearer *b_ptr;
+
+        rcu_read_lock();
+        b_ptr = rcu_dereference_rtnl(bearer_list[bearer_id]);
+        if (b_ptr) {
+                tipc_nmap_remove(&b_ptr->nodes, dest);
+                tipc_bcbearer_sort();
+                tipc_disc_remove_dest(b_ptr->link_req);
+        }
+        rcu_read_unlock();
 }
 
 /**
@@ -507,10 +521,16 @@ int tipc_l2_send_msg(struct sk_buff *buf, struct tipc_bearer *b,
  * The media send routine must not alter the buffer being passed in
  * as it may be needed for later retransmission!
  */
-void tipc_bearer_send(struct tipc_bearer *b, struct sk_buff *buf,
+void tipc_bearer_send(u32 bearer_id, struct sk_buff *buf,
                       struct tipc_media_addr *dest)
 {
-        b->media->send_msg(buf, b, dest);
+        struct tipc_bearer *b_ptr;
+
+        rcu_read_lock();
+        b_ptr = rcu_dereference_rtnl(bearer_list[bearer_id]);
+        if (likely(b_ptr))
+                b_ptr->media->send_msg(buf, b_ptr, dest);
+        rcu_read_unlock();
 }
 
 /**