Re: 2.6.23-rc8-mm2 - tcp_fastretrans_alert() WARNING

Ilpo Järvinen
2007-09-29T12:45:29Z

[-- Attachment #1: Type: TEXT/PLAIN, Size: 1533 bytes --]

On Fri, 28 Sep 2007, Ilpo Järvinen wrote:
> On Fri, 28 Sep 2007, Cedric Le Goater wrote:
>
> > I just found that warning in my logs. It seems that it's been
> > happening since rc7-mm1 at least.
> >
> > WARNING: at /home/legoater/linux/2.6.23-rc8-mm2/net/ipv4/tcp_input.c:2314 tcp_fastretrans_alert()
> >
> > Call Trace:
> > <IRQ> [<ffffffff8040fdc3>] tcp_ack+0xcd6/0x1894
> > ...snip...
>
> ...Thanks for the report, I'll have look what could still break
> fackets_out...

I think this one is now clear to me, tcp_fragment/collapse adjusts
fackets_out (incorrectly) also for reno flow when there were some dupACKs
that made sacked_out != 0. Could you please try if patch below proves all
them to be of non-SACK origin... In case that's true, it's rather
harmless, I'll send a fix on Monday or so (this would anyway be needed)...
If you find out that them occur with SACK enabled flow, that would be
more interesting and requires more digging...

--
i.

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 2286361..e642779 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2311,8 +2311,10 @@ tcp_fastretrans_alert(struct sock *sk, int pkts_acked, int flag)
if (!tp->packets_out)
tp->sacked_out = 0;

- if (WARN_ON(!tp->sacked_out && tp->fackets_out))
+ if (WARN_ON(!tp->sacked_out && tp->fackets_out)) {
+ printk(KERN_ERR "TCP %d\n", tcp_is_reno(tp));
tp->fackets_out = 0;
+ }

/* Now state machine starts.
* A. ECE, hence prohibit cwnd undoing, the reduction is required. */