ipvs: reorganize dest trash

All dests will go to trash, no exceptions.
But we have to use new list node t_list for this, due
to RCU changes in following patches. Dests will wait there
initial grace period and later all conns and schedulers to
put their reference. The dests don't get reference for
staying in dest trash as before.

	As result, we do not load ip_vs_dest_put with
extra checks for last refcnt and the schedulers do not
need to play games with atomic_inc_not_zero while
selecting best destination.
Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>

include/net/ip_vs.h

@@ -749,6 +749,8 @@ struct ip_vs_dest_dst {
 	struct rcu_head		rcu_head;
 };
 
+/* In grace period after removing */
+#define IP_VS_DEST_STATE_REMOVING	0x01
 /*
  *	The real server destination forwarding entry
  *	with ip address, port number, and so on.
@@ -766,6 +768,7 @@ struct ip_vs_dest {
 
 	atomic_t		refcnt;		/* reference counter */
 	struct ip_vs_stats      stats;          /* statistics */
+	unsigned long		state;		/* state flags */
 
 	/* connection counters and thresholds */
 	atomic_t		activeconns;	/* active connections */
@@ -785,6 +788,7 @@ struct ip_vs_dest {
 	union nf_inet_addr	vaddr;		/* virtual IP address */
 	__u32			vfwmark;	/* firewall mark of service */
 
+	struct list_head	t_list;		/* in dest_trash */
 	struct rcu_head		rcu_head;
 	unsigned int		in_rs_table:1;	/* we are in rs_table */
 };
@@ -912,6 +916,9 @@ struct ipvs_master_sync_state {
 	struct netns_ipvs	*ipvs;
 };
 
+/* How much time to keep dests in trash */
+#define IP_VS_DEST_TRASH_PERIOD		(120 * HZ)
+
 /* IPVS in network namespace */
 struct netns_ipvs {
 	int			gen;		/* Generation */
@@ -961,6 +968,8 @@ struct netns_ipvs {
 
 	/* Trash for destinations */
 	struct list_head	dest_trash;
+	spinlock_t		dest_trash_lock;
+	struct timer_list	dest_trash_timer; /* expiration timer */
 	/* Service counters */
 	atomic_t		ftpsvc_counter;
 	atomic_t		nullsvc_counter;