Problem: Active TCP connection aborts for no reason

* Problem: Active TCP connection  aborts  for no reason
@ 2003-10-15 22:32 Veeriah Vijay-A19819
  2003-10-16  4:56 ` David S. Miller
  0 siblings, 1 reply; 3+ messages in thread
From: Veeriah Vijay-A19819 @ 2003-10-15 22:32 UTC (permalink / raw)
  To: linux-kernel

I am using 2.4.7 kernel and seem to have a problem where my TCP connection aborts
when both the client and the server are, perfectly fine, up and running and sending 
data to each other. I have enabled keepalive on both the client and server side.

I was able to reproduce this problem by doing the following.
I  setup the tcp parameters to be as follows :
              tcp_keepalive_time =  2
              tcp_keepalive_probes = 1
              tcp_keepalive_intvl = 3
My server and client send data to each other approximately every 2 seconds.

>From tcpdump output I figured out the following.  After a keepalive_probe is sent out (at the expiry of  keepalive_time)
if it is immediately followed by some valid data, then the ack for the keepalive_probe from the remote side does 
not seem to reset the probes_out to 0. Because of  this when the keepalive_timer expires 
the next time it RSTs the connection.

The following code in tcp_input.c, seems to be the problem
	if ((prior_packets = tp->packets_out) == 0)
		goto no_queue;
            ....
	          return 1;

            no_queue:
                      tp->probes_out = 0
            ....

Since in my case prior_packets is not 0, because of the valid data, probes_out is not being reset.

In tcp_timer.c, the following code seems to reset the connection on the next keepalive
timer expiry,
    if (!tp->keepalive_probes && tp->probes_out >= sysctl_tcp_keepalive_probes) ||
         ...)
    {
	tcp_SEnd_Active_reset (sk, GFP_ATOMIC);
	tcp_write_err(sk);
	goto out;
    }

Can somebody let me know  if  I am missing something here or is it a genuine problem that 
has been fixed in a later release.

I can provide the tcpdump if need be.

Thanks,
Vijay

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