Re: [PATCH 2.6.5] Re: Fw: Stack sends SYN/ACKs even though accept queue is full]

[Nivedita Singhvi <niv@xxxxxxxxxx>]

> Attaching a patch which adds a sysctl to turn off this
> behaviour.   Could you test this, please?  Patch against
> 2.6.5 vanilla kernel.  If you need a 2.4 version, let me
> know. 

Oops, Andrew pointed out that my mailer had done
the nasty and wrapped my patch. Resending..

thanks,
Nivedita

diff -urN linux-2.6.5/include/linux/sysctl.h
linux-2.6.5synq/include/linux/sysctl.h
--- linux-2.6.5/include/linux/sysctl.h  2004-04-03 19:37:23.000000000 -0800
+++ linux-2.6.5synq/include/linux/sysctl.h      2004-04-30 15:24:12.000000000 
-0700
@@ -323,6 +323,7 @@
        NET_IPV4_IPFRAG_SECRET_INTERVAL=94,
        NET_TCP_WESTWOOD=95,
        NET_IPV4_IGMP_MAX_MSF=96,
+       NET_TCP_PRELOAD_SYNQ=97,
};

enum {
diff -urN linux-2.6.5/include/net/tcp.h
linux-2.6.5synq/include/net/tcp.h
--- linux-2.6.5/include/net/tcp.h       2004-04-03 19:36:18.000000000 -0800
+++ linux-2.6.5synq/include/net/tcp.h   2004-04-30 13:55:18.000000000 -0700
@@ -583,6 +583,7 @@
extern int sysctl_tcp_frto;
extern int sysctl_tcp_low_latency;
extern int sysctl_tcp_westwood;
+extern int sysctl_tcp_preload_synq;

extern atomic_t tcp_memory_allocated;
extern atomic_t tcp_sockets_allocated;
diff -urN linux-2.6.5/net/ipv4/sysctl_net_ipv4.c
linux-2.6.5synq/net/ipv4/sysctl_net_ipv4.c
--- linux-2.6.5/net/ipv4/sysctl_net_ipv4.c	2004-04-03 19:37:37.000000000 -0800
+++ linux-2.6.5synq/net/ipv4/sysctl_net_ipv4.c	2004-04-30 16:16:57.000000000 -0700
@@ -601,6 +601,14 @@
		.mode		= 0644,
		.proc_handler	= &proc_dointvec,
	},
+	{
+		.ctl_name	= NET_TCP_PRELOAD_SYNQ, 
+		.procname	= "tcp_preload_synq",
+		.data		= &sysctl_tcp_preload_synq,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= &proc_dointvec,
+	},
	{ .ctl_name = 0 }
};

diff -urN linux-2.6.5/net/ipv4/tcp_ipv4.c
linux-2.6.5synq/net/ipv4/tcp_ipv4.c
--- linux-2.6.5/net/ipv4/tcp_ipv4.c     2004-04-03 19:36:55.000000000 -0800
+++ linux-2.6.5synq/net/ipv4/tcp_ipv4.c 2004-04-30 15:51:38.000000000 -0700
@@ -78,6 +78,7 @@
extern int sysctl_ip_dynaddr;
int sysctl_tcp_tw_reuse;
int sysctl_tcp_low_latency;
+int sysctl_tcp_preload_synq = 1;

/* Check TCP sequence numbers in ICMP packets. */
#define ICMP_MIN_LENGTH 8
@@ -1442,8 +1443,11 @@
         * clogging syn queue with openreqs with exponentially increasing
         * timeout.
         */
-       if (tcp_acceptq_is_full(sk) && tcp_synq_young(sk) > 1)
-               goto drop;
+       if (tcp_acceptq_is_full(sk)) {
+               if (!sysctl_tcp_preload_synq ||
+                  (sysctl_tcp_preload_synq && (tcp_synq_young(sk) > 1)))
+                       goto drop;
+       }

        req = tcp_openreq_alloc();
        if (!req)
@@ -2683,4 +2687,5 @@
EXPORT_SYMBOL(sysctl_local_port_range);
EXPORT_SYMBOL(sysctl_max_syn_backlog);
EXPORT_SYMBOL(sysctl_tcp_low_latency);
+EXPORT_SYMBOL(sysctl_tcp_preload_synq);
#endif