[PATCH] ipvs: fix the connection sync failed in some cases

[guodeqing <geffrey.guo@xxxxxxxxxx>]

The sync_thread_backup only checks sk_receive_queue is empty or not,
there is a situation which cannot sync the connection entries when
sk_receive_queue is empty and sk_rmem_alloc is larger than sk_rcvbuf,
the sync packets are dropped in __udp_enqueue_schedule_skb, this is
because the packets in reader_queue is not read, so the rmem is
not reclaimed.

Here I add the check of whether the reader_queue of the udp sock is
empty or not to solve this problem.

Fixes: 7c13f97ffde6 ("udp: do fwd memory scheduling on dequeue")
Reported-by: zhouxudong <zhouxudong8@xxxxxxxxxx>
Signed-off-by: guodeqing <geffrey.guo@xxxxxxxxxx>
---
 net/netfilter/ipvs/ip_vs_sync.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/net/netfilter/ipvs/ip_vs_sync.c b/net/netfilter/ipvs/ip_vs_sync.c
index 605e0f6..abe8d63 100644
--- a/net/netfilter/ipvs/ip_vs_sync.c
+++ b/net/netfilter/ipvs/ip_vs_sync.c
@@ -1717,6 +1717,8 @@ static int sync_thread_backup(void *data)
 {
        struct ip_vs_sync_thread_data *tinfo = data;
        struct netns_ipvs *ipvs = tinfo->ipvs;
+       struct sock *sk = tinfo->sock->sk;
+       struct udp_sock *up = udp_sk(sk);
        int len;
 
        pr_info("sync thread started: state = BACKUP, mcast_ifn = %s, "
@@ -1724,12 +1726,14 @@ static int sync_thread_backup(void *data)
                ipvs->bcfg.mcast_ifn, ipvs->bcfg.syncid, tinfo->id);
 
        while (!kthread_should_stop()) {
-               wait_event_interruptible(*sk_sleep(tinfo->sock->sk),
-                        !skb_queue_empty(&tinfo->sock->sk->sk_receive_queue)
-                        || kthread_should_stop());
+               wait_event_interruptible(*sk_sleep(sk),
+                                        
!skb_queue_empty(&sk->sk_receive_queue) ||
+                                        !skb_queue_empty(&up->reader_queue) ||
+                                        kthread_should_stop());
 
                /* do we have data now? */
-               while (!skb_queue_empty(&(tinfo->sock->sk->sk_receive_queue))) {
+               while (!skb_queue_empty(&sk->sk_receive_queue) ||
+                      !skb_queue_empty(&up->reader_queue)) {
                        len = ip_vs_receive(tinfo->sock, tinfo->buf,
                                        ipvs->bcfg.sync_maxlen);
                        if (len <= 0) {
-- 
2.7.4