tipc: Fix problem with missing link in "tipc-config -l" output

Removes a race condition that could cause TIPC's internal counter
of the number of links it has to neighboring nodes to have the
incorrect value if two independent threads of control simultaneously
create new link endpoints connecting to two different nodes using two
different bearers. Such under counting would result in TIPC failing to
list the final link(s) in its response to a configuration request to
list all of the node's links. The counter is now updated atomically
to ensure that simultaneous increments do not interfere with each
other.

Thanks go to Peter Butler <pbutler@pt.com> for his assistance in
diagnosing and fixing this problem.

Signed-off-by: Allan Stephens <Allan.Stephens@windriver.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/net/tipc/node.c b/net/tipc/node.c
index 713ab5d7c54f..a24fad32345e 100644
--- a/net/tipc/node.c
+++ b/net/tipc/node.c
@@ -233,7 +233,7 @@ struct tipc_node *tipc_node_attach_link(struct link *l_ptr)
 
                 if (!n_ptr->links[bearer_id]) {
                         n_ptr->links[bearer_id] = l_ptr;
-                        tipc_net.links++;
+                        atomic_inc(&tipc_net.links);
                         n_ptr->link_cnt++;
                         return n_ptr;
                 }
@@ -247,7 +247,7 @@ struct tipc_node *tipc_node_attach_link(struct link *l_ptr)
 void tipc_node_detach_link(struct tipc_node *n_ptr, struct link *l_ptr)
 {
         n_ptr->links[l_ptr->b_ptr->identity] = NULL;
-        tipc_net.links--;
+        atomic_dec(&tipc_net.links);
         n_ptr->link_cnt--;
 }
 
@@ -450,7 +450,8 @@ struct sk_buff *tipc_node_get_links(const void *req_tlv_area, int req_tlv_space)
 
         /* Get space for all unicast links + multicast link */
 
-        payload_size = TLV_SPACE(sizeof(link_info)) * (tipc_net.links + 1);
+        payload_size = TLV_SPACE(sizeof(link_info)) *
+                (atomic_read(&tipc_net.links) + 1);
         if (payload_size > 32768u) {
                 read_unlock_bh(&tipc_net_lock);
                 return tipc_cfg_reply_error_string(TIPC_CFG_NOT_SUPPORTED