ipvs: Put backup thread on mcast socket wait queue

Instead of doing an endless loop with sleeping for one second, we now put the
backup thread onto the mcast socket wait queue and it gets woken up as soon as
we have data to process.

Signed-off-by: Sven Wegener <sven.wegener@stealer.net>
Acked-by: Simon Horman <horms@verge.net.au>
diff --git a/net/ipv4/ipvs/ip_vs_sync.c b/net/ipv4/ipvs/ip_vs_sync.c
index 550563a..cf5ed75 100644
--- a/net/ipv4/ipvs/ip_vs_sync.c
+++ b/net/ipv4/ipvs/ip_vs_sync.c
@@ -29,6 +29,7 @@
 #include <linux/udp.h>
 #include <linux/err.h>
 #include <linux/kthread.h>
+#include <linux/wait.h>
 
 #include <net/ip.h>
 #include <net/sock.h>
@@ -772,6 +773,10 @@
 		   ip_vs_backup_mcast_ifn, ip_vs_backup_syncid);
 
 	while (!kthread_should_stop()) {
+		wait_event_interruptible(*tinfo->sock->sk->sk_sleep,
+			 !skb_queue_empty(&tinfo->sock->sk->sk_receive_queue)
+			 || kthread_should_stop());
+
 		/* do we have data now? */
 		while (!skb_queue_empty(&(tinfo->sock->sk->sk_receive_queue))) {
 			len = ip_vs_receive(tinfo->sock, tinfo->buf,
@@ -787,8 +792,6 @@
 			ip_vs_process_message(tinfo->buf, len);
 			local_bh_enable();
 		}
-
-		msleep_interruptible(1000);
 	}
 
 	/* release the sending multicast socket */