Re: [PATCH] netfilter/ipvs: queue delayed work to expire no destination connections if expire_nodest_conn=1

[Julian Anastasov <ja@ssi.bg>]

	Hello,

On Wed, 27 May 2020, Andrew Sy Kim wrote:

> When expire_nodest_conn=1 and a destination is deleted, IPVS does not
> expire the existing connections until the next matching incoming packet.
> If there are many connection entries from a single client to a single
> destination, many packets may get dropped before all the connections are
> expired (more likely with lots of UDP traffic). An optimization can be
> made where upon deletion of a destination, IPVS queues up delayed work
> to immediately expire any connections with a deleted destination. This
> ensures any reused source ports from a client (within the IPVS timeouts)
> are scheduled to new real servers instead of silently dropped.
> 
> Signed-off-by: Andrew Sy Kim <kim.andrewsy@gmail.com>
> ---
>  include/net/ip_vs.h             |  9 ++++++
>  net/netfilter/ipvs/ip_vs_conn.c | 53 +++++++++++++++++++++++++++++++++
>  net/netfilter/ipvs/ip_vs_core.c | 44 +++++++++++----------------
>  net/netfilter/ipvs/ip_vs_ctl.c  | 12 ++++++++
>  4 files changed, 92 insertions(+), 26 deletions(-)
> 
> diff --git a/include/net/ip_vs.h b/include/net/ip_vs.h
> index 83be2d93b407..1636100f7da5 100644
> --- a/include/net/ip_vs.h
> +++ b/include/net/ip_vs.h
> @@ -884,6 +884,9 @@ struct netns_ipvs {
>  	atomic_t		nullsvc_counter;
>  	atomic_t		conn_out_counter;
>  
> +	/* delayed work for expiring no dest connections */
> +	struct delayed_work	expire_nodest_conn_work;

	All expire_nodest_conn code should be under CONFIG_SYSCTL,
so this should go below.

> +
>  #ifdef CONFIG_SYSCTL
>  	/* 1/rate drop and drop-entry variables */
>  	struct delayed_work	defense_work;   /* Work handler */
> @@ -1049,6 +1052,11 @@ static inline int sysctl_conn_reuse_mode(struct netns_ipvs *ipvs)
>  	return ipvs->sysctl_conn_reuse_mode;
>  }
>  
> +static inline int sysctl_expire_nodest_conn(struct netns_ipvs *ipvs)
> +{
> +	return ipvs->sysctl_expire_nodest_conn;
> +}
> +

	This is the CONFIG_SYSCTL code, you have to move the
empty function for the !CONFIG_SYSCTL case too. In general, we
try to hide such ifdefs in ip_vs.h, still the .c files can
ifdef whole functions. As result, for all these sysctl vars
we have two function variants depending on CONFIG_SYSCTL.

>  static inline int sysctl_schedule_icmp(struct netns_ipvs *ipvs)
>  {
>  	return ipvs->sysctl_schedule_icmp;
> @@ -1232,6 +1240,7 @@ struct ip_vs_conn *ip_vs_conn_new(const struct ip_vs_conn_param *p, int dest_af,
>  				  __be16 dport, unsigned int flags,
>  				  struct ip_vs_dest *dest, __u32 fwmark);
>  void ip_vs_conn_expire_now(struct ip_vs_conn *cp);
> +void expire_nodest_conn_handler(struct work_struct *work);

	Keep this in ip_vs_ctl.c under CONFIG_SYSCTL.
Here add ip_vs_expire_nodest_conn_flush(struct netns_ipvs *ipvs);
under CONFIG_SYSCTL.

>  const char *ip_vs_state_name(const struct ip_vs_conn *cp);
>  
> diff --git a/net/netfilter/ipvs/ip_vs_conn.c b/net/netfilter/ipvs/ip_vs_conn.c
> index 02f2f636798d..5e802b7fabbb 100644
> --- a/net/netfilter/ipvs/ip_vs_conn.c
> +++ b/net/netfilter/ipvs/ip_vs_conn.c
> @@ -28,6 +28,7 @@
>  #include <linux/module.h>
>  #include <linux/vmalloc.h>
>  #include <linux/proc_fs.h>		/* for proc_net_* */
> +#include <linux/workqueue.h>
>  #include <linux/slab.h>
>  #include <linux/seq_file.h>
>  #include <linux/jhash.h>
> @@ -1366,6 +1367,58 @@ static void ip_vs_conn_flush(struct netns_ipvs *ipvs)
>  		goto flush_again;
>  	}
>  }
> +
> +/*	Handler for delayed work for expiring no
> + *	destination connections
> + */
> +void expire_nodest_conn_handler(struct work_struct *work)
> +{
> +	int idx;
> +	struct ip_vs_conn *cp, *cp_c;
> +	struct ip_vs_dest *dest;
> +	struct netns_ipvs *ipvs;
> +
> +	ipvs = container_of(work, struct netns_ipvs,
> +			    expire_nodest_conn_work.work);
> +
> +	/* netns clean up started, aborted delayed work */
> +	if (!ipvs->enable)
> +		return;

	This is of no use here, it should be near
cond_resched_rcu(), so that we can abort immediately,
not after seconds...

> +
> +	/* only start delayed work if expire_nodest_conn=1 */
> +	if (!ipvs->sysctl_expire_nodest_conn)
> +		return;
> +

	May be not needed because work was queued after
such check. And we want to avoid using an ipvs field,
we prefer the sysctl_expire_nodest_conn() function
because such fields should not be compiled when
!CONFIG_SYSCTL, which is not the case for many of them
but this needs special cleanup with another patch...

	Just like ip_vs_random_dropentry(), keep the below
logic in ip_vs_conn.c in separate function, eg.
ip_vs_expire_nodest_conn_flush(ipvs), under CONFIG_SYSCTL,
called from the work callback which is in ip_vs_ctl.c.
We want functions that walk ip_vs_conn_tab in ip_vs_conn.c.

> +	rcu_read_lock();
> +	for (idx = 0; idx < ip_vs_conn_tab_size; idx++) {
> +		hlist_for_each_entry_rcu(cp, &ip_vs_conn_tab[idx], c_list) {
> +			if (cp->ipvs != ipvs)
> +				continue;
> +
> +			dest = cp->dest;
> +			if (!dest || (dest->flags & IP_VS_DEST_F_AVAILABLE))
> +				continue;
> +
> +			/* As timers are expired in LIFO order, restart
> +			 * the timer of controlling connection first, so
> +			 * that it is expired after us.
> +			 */
> +			cp_c = cp->control;
> +			/* cp->control is valid only with reference to cp */
> +			if (cp_c && __ip_vs_conn_get(cp)) {
> +				IP_VS_DBG(4, "del controlling connection\n");
> +				ip_vs_conn_expire_now(cp_c);
> +				__ip_vs_conn_put(cp);
> +			}
> +
> +			IP_VS_DBG(4, "del connection\n");
> +			ip_vs_conn_expire_now(cp);
> +		}
> +		cond_resched_rcu();
> +	}
> +	rcu_read_unlock();
> +}
> +
>  /*
>   * per netns init and exit
>   */
> diff --git a/net/netfilter/ipvs/ip_vs_core.c b/net/netfilter/ipvs/ip_vs_core.c
> index aa6a603a2425..c8389936d51a 100644
> --- a/net/netfilter/ipvs/ip_vs_core.c
> +++ b/net/netfilter/ipvs/ip_vs_core.c
> @@ -694,11 +694,6 @@ static int sysctl_nat_icmp_send(struct netns_ipvs *ipvs)
>  	return ipvs->sysctl_nat_icmp_send;
>  }
>  
> -static int sysctl_expire_nodest_conn(struct netns_ipvs *ipvs)
> -{
> -	return ipvs->sysctl_expire_nodest_conn;
> -}
> -
>  #else
>  

	At this place there is second sysctl_expire_nodest_conn()
that should be moved to ip_vs.h

>  static int sysctl_snat_reroute(struct netns_ipvs *ipvs) { return 0; }
> @@ -2095,36 +2090,33 @@ ip_vs_in(struct netns_ipvs *ipvs, unsigned int hooknum, struct sk_buff *skb, int
>  		}
>  	}
>  
> -	if (unlikely(!cp)) {
> -		int v;
> -
> -		if (!ip_vs_try_to_schedule(ipvs, af, skb, pd, &v, &cp, &iph))
> -			return v;
> -	}
> -
> -	IP_VS_DBG_PKT(11, af, pp, skb, iph.off, "Incoming packet");
> -
>  	/* Check the server status */
> -	if (cp->dest && !(cp->dest->flags & IP_VS_DEST_F_AVAILABLE)) {
> +	if (cp && cp->dest && !(cp->dest->flags & IP_VS_DEST_F_AVAILABLE)) {
>  		/* the destination server is not available */
>  
> -		__u32 flags = cp->flags;
> -
> -		/* when timer already started, silently drop the packet.*/
> -		if (timer_pending(&cp->timer))
> -			__ip_vs_conn_put(cp);
> -		else
> -			ip_vs_conn_put(cp);
> +		if (sysctl_expire_nodest_conn(ipvs)) {
> +			bool uses_ct = ip_vs_conn_uses_conntrack(cp, skb);
>  
> -		if (sysctl_expire_nodest_conn(ipvs) &&
> -		    !(flags & IP_VS_CONN_F_ONE_PACKET)) {
> -			/* try to expire the connection immediately */
>  			ip_vs_conn_expire_now(cp);
> +			__ip_vs_conn_put(cp);
> +			if (uses_ct)
> +				return NF_DROP;
> +			cp = NULL;
> +		} else {
> +			__ip_vs_conn_put(cp);
> +			return NF_DROP;
>  		}
> +	}
>  
> -		return NF_DROP;
> +	if (unlikely(!cp)) {
> +		int v;
> +
> +		if (!ip_vs_try_to_schedule(ipvs, af, skb, pd, &v, &cp, &iph))
> +			return v;
>  	}
>  
> +	IP_VS_DBG_PKT(11, af, pp, skb, iph.off, "Incoming packet");
> +
>  	ip_vs_in_stats(cp, skb);
>  	ip_vs_set_state(cp, IP_VS_DIR_INPUT, skb, pd);
>  	if (cp->packet_xmit)
> diff --git a/net/netfilter/ipvs/ip_vs_ctl.c b/net/netfilter/ipvs/ip_vs_ctl.c
> index 8d14a1acbc37..6eb1afa30c74 100644
> --- a/net/netfilter/ipvs/ip_vs_ctl.c
> +++ b/net/netfilter/ipvs/ip_vs_ctl.c
> @@ -1163,6 +1163,13 @@ static void __ip_vs_del_dest(struct netns_ipvs *ipvs, struct ip_vs_dest *dest,
>  	list_add(&dest->t_list, &ipvs->dest_trash);
>  	dest->idle_start = 0;
>  	spin_unlock_bh(&ipvs->dest_trash_lock);
> +
> +	/*	If expire_nodest_conn is enabled and we're not cleaning up,
> +	 *	queue up delayed work to expire all no destination connections
> +	 */
> +	if (sysctl_expire_nodest_conn(ipvs) && !cleanup)
> +		queue_delayed_work(system_long_wq,
> +				   &ipvs->expire_nodest_conn_work, 1);

	May be we should put this in ifdef CONFIG_SYSCTL.
Another option is to have ip_vs_enqueue_expire_nodest_conns()
in ip_vs.h, again in two variants, to avoid ifdef here.

>  }
>  
>  
> @@ -4065,6 +4072,10 @@ static int __net_init ip_vs_control_net_init_sysctl(struct netns_ipvs *ipvs)
>  	INIT_DELAYED_WORK(&ipvs->defense_work, defense_work_handler);
>  	schedule_delayed_work(&ipvs->defense_work, DEFENSE_TIMER_PERIOD);
>  
> +	/* Init delayed work for expiring no dest conn */
> +	INIT_DELAYED_WORK(&ipvs->expire_nodest_conn_work,
> +			  expire_nodest_conn_handler);
> +
>  	return 0;
>  }
>  
> @@ -4072,6 +4083,7 @@ static void __net_exit ip_vs_control_net_cleanup_sysctl(struct netns_ipvs *ipvs)
>  {
>  	struct net *net = ipvs->net;
>  
> +	cancel_delayed_work_sync(&ipvs->expire_nodest_conn_work);
>  	cancel_delayed_work_sync(&ipvs->defense_work);
>  	cancel_work_sync(&ipvs->defense_work.work);
>  	unregister_net_sysctl_table(ipvs->sysctl_hdr);
> -- 

Regards

--
Julian Anastasov <ja@ssi.bg>