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

["Guodeqing (A)" <geffrey.guo@huawei.com>]

I do a ipvs connection sync test in a 3.10 version kernel which has the 7c13f97ffde6 commit which succeed. I will modify the fixes information of the patch and replace the skb_queue_empty with skb_queue_empty_lockless.
Thanks.

-----邮件原件-----
发件人: Julian Anastasov [mailto:ja@ssi.bg] 
发送时间: Thursday, July 16, 2020 1:36
收件人: Guodeqing (A) <geffrey.guo@huawei.com>
抄送: wensong@linux-vs.org; horms@verge.net.au; pablo@netfilter.org; kadlec@netfilter.org; fw@strlen.de; davem@davemloft.net; kuba@kernel.org; netdev@vger.kernel.org; lvs-devel@vger.kernel.org; netfilter-devel@vger.kernel.org
主题: Re: [PATCH] ipvs: fix the connection sync failed in some cases


	Hello,

On Wed, 15 Jul 2020, guodeqing wrote:

> 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.

	Good catch. We missed this change in UDP...

> 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")

	Why this commit and not 2276f58ac589 which adds reader_queue to udp_poll() ? May be both?

> Reported-by: zhouxudong <zhouxudong8@huawei.com>
> Signed-off-by: guodeqing <geffrey.guo@huawei.com>
> ---
>  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) ||

	May be we should use skb_queue_empty_lockless for 5.4+ and skb_queue_empty() for backports to 4.14 and 4.19...

> +					 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)) {

	Here too

>  			len = ip_vs_receive(tinfo->sock, tinfo->buf,
>  					ipvs->bcfg.sync_maxlen);
>  			if (len <= 0) {
> --
> 2.7.4

Regards

--
Julian Anastasov <ja@ssi.bg>