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>
mariux64 · Mar 13, 2011 · 9df3b7e · 9df3b7e
1 parent 71092ea
commit 9df3b7e
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Showing 3 changed files with 8 additions and 6 deletions.
diff --git a/net/tipc/net.c b/net/tipc/net.c
@@ -2,7 +2,7 @@
  * net/tipc/net.c: TIPC network routing code
  *
  * Copyright (c) 1995-2006, Ericsson AB
- * Copyright (c) 2005, Wind River Systems
+ * Copyright (c) 2005, 2010-2011, Wind River Systems
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -115,6 +115,7 @@ static int net_start(void)
 	tipc_net.nodes = kcalloc(tipc_max_nodes + 1,
 				 sizeof(*tipc_net.nodes), GFP_ATOMIC);
 	tipc_net.highest_node = 0;
+	atomic_set(&tipc_net.links, 0);
 
 	return tipc_net.nodes ? 0 : -ENOMEM;
 }

diff --git a/net/tipc/net.h b/net/tipc/net.h
@@ -2,7 +2,7 @@
  * net/tipc/net.h: Include file for TIPC network routing code
  *
  * Copyright (c) 1995-2006, Ericsson AB
- * Copyright (c) 2005, Wind River Systems
+ * Copyright (c) 2005, 2010-2011, Wind River Systems
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -49,7 +49,7 @@ struct tipc_node;
 struct network {
 	struct tipc_node **nodes;
 	u32 highest_node;
-	u32 links;
+	atomic_t links;
 };
 
 

diff --git 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