tipc: purge tipc_net_lock lock

Now tipc routing hierarchy comprises the structures 'node', 'link'and
'bearer'. The whole hierarchy is protected by a big read/write lock,
tipc_net_lock, to ensure that nothing is added or removed while code
is accessing any of these structures. Obviously the locking policy
makes node, link and bearer components closely bound together so that
their relationship becomes unnecessarily complex. In the worst case,
such locking policy not only has a negative influence on performance,
but also it's prone to lead to deadlock occasionally.

In order o decouple the complex relationship between bearer and node
as well as link, the locking policy is adjusted as follows:

- Bearer level
  RTNL lock is used on update side, and RCU is used on read side.
  Meanwhile, all bearer instances including broadcast bearer are
  saved into bearer_list array.

- Node and link level
  All node instances are saved into two tipc_node_list and node_htable
  lists. The two lists are protected by node_list_lock on write side,
  and they are guarded with RCU lock on read side. All members in node
  structure including link instances are protected by node spin lock.

- The relationship between bearer and node
  When link accesses bearer, it first needs to find the bearer with
  its bearer identity from the bearer_list array. When bearer accesses
  node, it can iterate the node_htable hash list with the node
  address to find the corresponding node.

In the new locking policy, every component has its private locking
solution and the relationship between bearer and node is very simple,
that is, they can find each other with node address or bearer identity
from node_htable hash list or bearer_list array.

Until now above all changes have been done, so tipc_net_lock can be
removed safely.

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, 2 insertions, 4 deletions

diff --git a/net/tipc/bcast.c b/net/tipc/bcast.c
index 51dab96ddd5f..0f32226db483 100644
--- a/net/tipc/bcast.c
+++ b/net/tipc/bcast.c
@@ -273,7 +273,7 @@ exit:
 /**
  * tipc_bclink_update_link_state - update broadcast link state
  *
- * tipc_net_lock and node lock set
+ * RCU and node lock set
  */
 void tipc_bclink_update_link_state(struct tipc_node *n_ptr, u32 last_sent)
 {
@@ -335,8 +335,6 @@ void tipc_bclink_update_link_state(struct tipc_node *n_ptr, u32 last_sent)
  *
  * Delay any upcoming NACK by this node if another node has already
  * requested the first message this node is going to ask for.
- *
- * Only tipc_net_lock set.
  */
 static void bclink_peek_nack(struct tipc_msg *msg)
 {
@@ -408,7 +406,7 @@ static void bclink_accept_pkt(struct tipc_node *node, u32 seqno)
 /**
  * tipc_bclink_rcv - receive a broadcast packet, and deliver upwards
  *
- * tipc_net_lock is read_locked, no other locks set
+ * RCU is locked, no other locks set
  */
 void tipc_bclink_rcv(struct sk_buff *buf)
 {