Out of socket memory? (2.4.0-test11)

FWIW, the code that prints this is in ipv4/tcp_timer.c and it looks like it's a DoS attack countermeasure. Looks like you can tune it with sysctl_tcp_max_orphans, among other things. Here's the code from test11-pre4:

/* Do not allow orphaned sockets to eat all our resources.
* This is direct violation of TCP specs, but it is required
* to prevent DoS attacks. It is called when a retransmission timeout
* or zero probe timeout occurs on orphaned socket.
*
* Criterium is still not confirmed experimentally and may change.
* We kill the socket, if:
* 1. If number of orphaned sockets exceeds an administratively configured
* limit.
* 2. If we have strong memory pressure.
*/
static int tcp_out_of_resources(struct sock *sk, int do_reset)

{
    struct tcp_opt *tp = &(sk->tp_pinfo.af_tcp);
    int orphans = atomic_read(&tcp_orphan_count);
 
    /* If peer does not open window for long time, or did not transmit
     * anything for long time, penalize it. */
    if ((s32)(tcp_time_stamp - tp->lsndtime) > 2*TCP_RTO_MAX || !do_reset)
        orphans <<= 1;
 
    /* If some dubious ICMP arrived, penalize even more. */
    if (sk->err_soft)
        orphans <<= 1;
 
    if (orphans >= sysctl_tcp_max_orphans ||
        (sk->wmem_queued > SOCK_MIN_SNDBUF &&
         atomic_read(&tcp_memory_allocated) > sysctl_tcp_mem[2])) {
        if (net_ratelimit())
            printk(KERN_INFO "Out of socket memory\n");

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See Documentation/networking/ip-sysctl.txt for more info and tuning suggestions, esp. tcp_orphan_retries and tcp_max_orphans. An orphaned socket is one that has at least partially opened, but has not been fully accepted. You might try reducing tcp_orphan_retries.

It looks like you can view the current number of orphans at /proc/net/sockstat or something like that.

/*
* Report socket allocation statistics [[email protected]]
*/
int afinet_get_info(char *buffer, char **start, off_t offset, int length)

{
    /* From  net/socket.c  */
    extern int socket_get_info(char *, char **, off_t, int);
 
    int len  = socket_get_info(buffer,start,offset,length);
 
    len += sprintf(buffer+len,"TCP: inuse %d orphan %d tw %d alloc %d mem %d\n",
               fold_prot_inuse(&tcp_prot),
               atomic_read(&tcp_orphan_count), tcp_tw_count,
               atomic_read(&tcp_sockets_allocated),
               atomic_read(&tcp_memory_allocated));     

- Dan
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