Re: [PATCH] ipvs: Fix reuse connection if RS weight is 0
From: Julian Anastasov <ja@ssi.bg>
Date: 2021-10-25 18:12:45
Also in:
lkml, lvs-devel, netdev, netfilter-devel
Hello, On Mon, 25 Oct 2021, yangxingwu wrote:
Since commit dc7b3eb900aa ("ipvs: Fix reuse connection if real server is
dead"), new connections to dead servers are redistributed immediately to
new servers.
Then commit d752c3645717 ("ipvs: allow rescheduling of new connections when
port reuse is detected") disable expire_nodest_conn if conn_reuse_mode is
0. And new connection may be distributed to a real server with weight 0.Your change does not look correct to me. At the time expire_nodest_conn was created, it was not checked when weight is 0. At different places different terms are used but in short, we have two independent states for real server: - inhibited: weight=0 and no new connections should be served, packets for existing connections can be routed to server if it is still available and packets are not dropped by expire_nodest_conn. The new feature is that port reuse detection can redirect the new TCP connection into a new IPVS conn and to expire the existing cp/ct. - unavailable (!IP_VS_DEST_F_AVAILABLE): server is removed, can be temporary, drop traffic for existing connections but on expire_nodest_conn we can select different server The new conn_reuse_mode flag allows port reuse to be detected. Only then expire_nodest_conn has the opportunity with commit dc7b3eb900aa to check weight=0 and to consider the old traffic as finished. If a new server is selected, any retrans from previous connection would be considered as part from the new connection. It is a rapid way to switch server without checking with is_new_conn_expected() because we can not have many conns/conntracks to different servers.
quoted hunk ↗ jump to hunk
Signed-off-by: yangxingwu <redacted> --- Documentation/networking/ipvs-sysctl.rst | 3 +-- net/netfilter/ipvs/ip_vs_core.c | 5 +++-- 2 files changed, 4 insertions(+), 4 deletions(-)diff --git a/Documentation/networking/ipvs-sysctl.rst b/Documentation/networking/ipvs-sysctl.rst index 2afccc63856e..1cfbf1add2fc 100644 --- a/Documentation/networking/ipvs-sysctl.rst +++ b/Documentation/networking/ipvs-sysctl.rst@@ -37,8 +37,7 @@ conn_reuse_mode - INTEGER 0: disable any special handling on port reuse. The new connection will be delivered to the same real server that was - servicing the previous connection. This will effectively - disable expire_nodest_conn. + servicing the previous connection. bit 1: enable rescheduling of new connections when it is safe. That is, whenever expire_nodest_conn and for TCP sockets, whendiff --git a/net/netfilter/ipvs/ip_vs_core.c b/net/netfilter/ipvs/ip_vs_core.c index 128690c512df..9279aed69e23 100644 --- a/net/netfilter/ipvs/ip_vs_core.c +++ b/net/netfilter/ipvs/ip_vs_core.c@@ -2042,14 +2042,15 @@ ip_vs_in(struct netns_ipvs *ipvs, unsigned int hooknum, struct sk_buff *skb, int ipvs, af, skb, &iph); conn_reuse_mode = sysctl_conn_reuse_mode(ipvs); - if (conn_reuse_mode && !iph.fragoffs && is_new_conn(skb, &iph) && cp) { + if (!iph.fragoffs && is_new_conn(skb, &iph) && cp) { bool old_ct = false, resched = false; if (unlikely(sysctl_expire_nodest_conn(ipvs)) && cp->dest && unlikely(!atomic_read(&cp->dest->weight))) { resched = true; old_ct = ip_vs_conn_uses_old_conntrack(cp, skb); - } else if (is_new_conn_expected(cp, conn_reuse_mode)) { + } else if (conn_reuse_mode && + is_new_conn_expected(cp, conn_reuse_mode)) { old_ct = ip_vs_conn_uses_old_conntrack(cp, skb); if (!atomic_read(&cp->n_control)) { resched = true;-- 2.30.2
Regards -- Julian Anastasov [off-list ref]