Messages in this thread Patch in this message | | | Date | Fri, 3 Dec 2010 14:39:03 +0100 | From | Holger Eitzenberger <> | Subject | ctnetlink loop |
| |
Hi,
I see a problem with how ctnetlink GET requests are being processed in the kernel (2.6.32.24) under high load.
Initially I saw this problem on a large performance testing system when getting HTTP proxy performance numbers, but lately there have been two reports on large customers boxes (both many-core with 10G NICs).
The sympton is Netlink looping around nfnetlink_rcv_msg(), which is just because netlink_unicast() came back with -EAGAIN when trying to write the newly created Netlink skb to the SK receive buffer in ctnetlink_get_conntrack(). In this case a (possibly) infinit loop is entered. Mostly infinit in fact in case the userland party trying to receive those messages may be stuck in the sendmsg() call, being unable to read anything if being single threaded.
I tried to reproduce several times, a few times the loop disappeared and the box proceeded normally after some time. I have no explanation for this.
The attached patch tries to solve it by simple not trying again to netlink_unicast() the reply skb and just fail with -ENOBUFS. The reasoning is that at the point a Netlink overrun is observed it seems counter intuitive to insist on sending one more Netlink message.
I checked for possible side effects to other Netlink requests, please check.
The patch applies to net-next-2.6.
Feedback appreciated.
/holger
nfnetlink: avoid unbound loop on busy Netlink socket
I see a problem with how ctnetlink GET requests are being processed in the kernel (2.6.32.24) under high load.
The sympton is Netlink looping around nfnetlink_rcv_msg(), which is just because netlink_unicast() came back with EAGAIN when trying to write the newly created Netlink skb to the SK receive buffer in ctnetlink_get_conntrack(). In this case a (possibly) infinit loop is entered. Mostly infinit I think in case the userland party trying to receive those messages may be stuck in the sendmsg() call, being unable to read anything if being single threaded.
I tried to reproduce several times, a few times the loop disappeared and the box proceeded normally after some minutes. I have no explanation for this.
The attached patch tries to solve it by simple not trying again to netlink_unicast() the reply skb and just fail with -ENOBUFS. The reasoning is that at the point a Netlink overrun is detected it seems counter intuitive to insist on sending one more Netlink message.
Signed-off-by: Holger Eitzenberger <holger@eitzenberger.org>
Index: net-next-2.6/net/netfilter/nfnetlink.c =================================================================== --- net-next-2.6.orig/net/netfilter/nfnetlink.c 2010-12-03 14:33:32.000000000 +0100 +++ net-next-2.6/net/netfilter/nfnetlink.c 2010-12-03 14:34:21.000000000 +0100 @@ -138,7 +138,6 @@ return 0; type = nlh->nlmsg_type; -replay: ss = nfnetlink_get_subsys(type); if (!ss) { #ifdef CONFIG_MODULES @@ -169,7 +168,7 @@ err = nc->call(net->nfnl, skb, nlh, (const struct nlattr **)cda); if (err == -EAGAIN) - goto replay; + err = -ENOBUFS; return err; } } | |