tipc: resolve race problem at unicast message reception

TIPC handles message cardinality and sequencing at the link layer,
before passing messages upwards to the destination sockets. During the
upcall from link to socket no locks are held. It is therefore possible,
and we see it happen occasionally, that messages arriving in different
threads and delivered in sequence still bypass each other before they
reach the destination socket. This must not happen, since it violates
the sequentiality guarantee.

We solve this by adding a new input buffer queue to the link structure.
Arriving messages are added safely to the tail of that queue by the
link, while the head of the queue is consumed, also safely, by the
receiving socket. Sequentiality is secured per socket by only allowing
buffers to be dequeued inside the socket lock. Since there may be multiple
simultaneous readers of the queue, we use a 'filter' parameter to reduce
the risk that they peek the same buffer from the queue, hence also
reducing the risk of contention on the receiving socket locks.

This solves the sequentiality problem, and seems to cause no measurable
performance degradation.

A nice side effect of this change is that lock handling in the functions
tipc_rcv() and tipc_bcast_rcv() now becomes uniform, something that
will enable future simplifications of those functions.

Reviewed-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 1 deletions

diff --git a/net/tipc/name_distr.h b/net/tipc/name_distr.h
index 5ec10b59527b..dd2d9fd80da2 100644
--- a/net/tipc/name_distr.h
+++ b/net/tipc/name_distr.h
@@ -71,7 +71,7 @@ struct sk_buff *tipc_named_publish(struct net *net, struct publication *publ);
 struct sk_buff *tipc_named_withdraw(struct net *net, struct publication *publ);
 void named_cluster_distribute(struct net *net, struct sk_buff *buf);
 void tipc_named_node_up(struct net *net, u32 dnode);
-void tipc_named_rcv(struct net *net, struct sk_buff *buf);
+void tipc_named_rcv(struct net *net, struct sk_buff_head *msg_queue);
 void tipc_named_reinit(struct net *net);
 void tipc_named_process_backlog(struct net *net);
 void tipc_publ_notify(struct net *net, struct list_head *nsub_list, u32 addr);