net: sched: change tcf block reference counter type to refcount_t

As a preparation for removing rtnl lock dependency from rules update path,
change tcf block reference counter type to refcount_t to allow modification
by concurrent users.

In block put function perform decrement and check reference counter once to
accommodate concurrent modification by unlocked users. After this change
tcf_chain_put at the end of block put function is called with
block->refcnt==0 and will deallocate block after the last chain is
released, so there is no need to manually deallocate block in this case.
However, if block reference counter reached 0 and there are no chains to
release, block must still be deallocated manually.

Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sch_generic.h

@@ -345,7 +345,7 @@ struct tcf_chain {
 struct tcf_block {
 	struct list_head chain_list;
 	u32 index; /* block index for shared blocks */
-	unsigned int refcnt;
+	refcount_t refcnt;
 	struct net *net;
 	struct Qdisc *q;
 	struct list_head cb_list;