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, 73 insertions, 0 deletions

diff --git a/net/tipc/msg.h b/net/tipc/msg.h
index 6070299..ab46726 100644
--- a/net/tipc/msg.h
+++ b/net/tipc/msg.h
@@ -45,6 +45,7 @@
  * Note: Some items are also used with TIPC internal message headers
  */
 #define TIPC_VERSION              2
+struct plist;
 
 /*
  * Payload message users are defined in TIPC's public API:
@@ -759,10 +760,82 @@ int tipc_buf_append(struct sk_buff **headbuf, struct sk_buff **buf);
 bool tipc_msg_bundle(struct sk_buff_head *list, struct sk_buff *skb, u32 mtu);
 bool tipc_msg_make_bundle(struct sk_buff_head *list,
 			  struct sk_buff *skb, u32 mtu, u32 dnode);
+bool tipc_msg_extract(struct sk_buff *skb, struct sk_buff **iskb, int *pos);
 int tipc_msg_build(struct tipc_msg *mhdr, struct msghdr *m,
 		   int offset, int dsz, int mtu, struct sk_buff_head *list);
 bool tipc_msg_lookup_dest(struct net *net, struct sk_buff *skb, u32 *dnode,
 			  int *err);
 struct sk_buff *tipc_msg_reassemble(struct sk_buff_head *list);
 
+/* tipc_skb_peek_port(): find a destination port, ignoring all destinations
+ *                       up to and including 'filter'.
+ * Note: ignoring previously tried destinations minimizes the risk of
+ *       contention on the socket lock
+ * @list: list to be peeked in
+ * @filter: last destination to be ignored from search
+ * Returns a destination port number, of applicable.
+ */
+static inline u32 tipc_skb_peek_port(struct sk_buff_head *list, u32 filter)
+{
+	struct sk_buff *skb;
+	u32 dport = 0;
+	bool ignore = true;
+
+	spin_lock_bh(&list->lock);
+	skb_queue_walk(list, skb) {
+		dport = msg_destport(buf_msg(skb));
+		if (!filter || skb_queue_is_last(list, skb))
+			break;
+		if (dport == filter)
+			ignore = false;
+		else if (!ignore)
+			break;
+	}
+	spin_unlock_bh(&list->lock);
+	return dport;
+}
+
+/* tipc_skb_dequeue(): unlink first buffer with dest 'dport' from list
+ * @list: list to be unlinked from
+ * @dport: selection criteria for buffer to unlink
+ */
+static inline struct sk_buff *tipc_skb_dequeue(struct sk_buff_head *list,
+					       u32 dport)
+{
+	struct sk_buff *_skb, *tmp, *skb = NULL;
+
+	spin_lock_bh(&list->lock);
+	skb_queue_walk_safe(list, _skb, tmp) {
+		if (msg_destport(buf_msg(_skb)) == dport) {
+			__skb_unlink(_skb, list);
+			skb = _skb;
+			break;
+		}
+	}
+	spin_unlock_bh(&list->lock);
+	return skb;
+}
+
+/* tipc_skb_queue_tail(): add buffer to tail of list;
+ * @list: list to be appended to
+ * @skb: buffer to append. Always appended
+ * @dport: the destination port of the buffer
+ * returns true if dport differs from previous destination
+ */
+static inline bool tipc_skb_queue_tail(struct sk_buff_head *list,
+				       struct sk_buff *skb, u32 dport)
+{
+	struct sk_buff *_skb = NULL;
+	bool rv = false;
+
+	spin_lock_bh(&list->lock);
+	_skb = skb_peek_tail(list);
+	if (!_skb || (msg_destport(buf_msg(_skb)) != dport) ||
+	    (skb_queue_len(list) > 32))
+		rv = true;
+	__skb_queue_tail(list, skb);
+	spin_unlock_bh(&list->lock);
+	return rv;
+}
+
 #endif