From: Stephen Hemminger <shemminger@linux-foundation.org>
To: "Lior Dotan" <liodot@gmail.com>
Cc: netdev@vger.kernel.org
Subject: Re: [PATCH-2.4] Fix divide by 0 in vegas_cong_avoid()
Date: Tue, 29 May 2007 08:05:34 -0700 [thread overview]
Message-ID: <20070529080534.5692bad8@freepuppy> (raw)
In-Reply-To: <a5bf86a80705290218t5e8605d3m9750d9dae6d96112@mail.gmail.com>
On Tue, 29 May 2007 12:18:19 +0300
"Lior Dotan" <liodot@gmail.com> wrote:
> Hi,
>
> I had a divide by zero on kernel 2.4.33 running with Vegas enabled.
> The KDB back trace is:
> kdb> bt
> Stack traceback for pid 0
> 0x403a6000 0 0 1 0 R 0x403a6370 *swapper
> EBP EIP Function (args)
> 0x403a7d48 0x4026ae51 vegas_cong_avoid+0x111 (0x5f3bb638, 0x73c92cbb, 0xffffffff
> , 0x73c92cbb, 0xf28d0275)
> kernel .text 0x40100000 0x4026ad40 0x4026aef0
> 0x403a7d8c 0x4026bb67 tcp_ack+0x307 (0x5f3bb560, 0x581985c0, 0x18e, 0x4023e765,
> 0x5c369044)
> kernel .text 0x40100000 0x4026b860 0x4026be20
> 0x403a7ddc 0x4026e771 tcp_rcv_established+0x461 (0x5f3bb560, 0x581985c0, 0x5c369
> 044, 0x2c, 0x5f3bb638)
> kernel .text 0x40100000 0x4026e310 0x4026ed80
> 0x403a7e00 0x40277c2f tcp_v4_do_rcv+0x14f (0x5f3bb560, 0x581985c0, 0x0, 0x403a7e
> 50, 0x4024bb42)
> kernel .text 0x40100000 0x40277ae0 0x40277c40
> <Rest was cut for readability>
> What happens is that vegas_rtt_calc() gets rtt as -1, so when it adds
> 1 the rtt is set to zero.
> It seems that the -1 came from tcp_clean_rtx_queue() so I made this
> small patch to fix the problem. I think it is also relevant to 2.6.
Seems like fixing the -1 would be better. Perhaps NTP reset
the clock?
>
> Don't perform congestion avoidance on packets that we didn't calculate
> there RTT, as this may result in a divide by zero later on.
>
> Signed-off-by: Lior Dotan <liodot@gmail.com>
> ---
>
> diff -up net/ipv4/tcp_input.c.orig net/ipv4/tcp_input.c
> --- net/ipv4/tcp_input.c.orig 2007-05-29 11:43:37.000000000 +0300
> +++ net/ipv4/tcp_input.c 2007-05-29 11:20:21.000000000 +0300
> @@ -2425,6 +2424,7 @@ static int tcp_clean_rtx_queue(struct so
> tp->retrans_out--;
> acked |= FLAG_RETRANS_DATA_ACKED;
> seq_rtt = -1;
> + acked &= ~FLAG_DATA_ACKED;
> } else if (seq_rtt < 0)
> seq_rtt = now - scb->when;
> if(sacked & TCPCB_SACKED_ACKED)
> -
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--
Stephen Hemminger <shemminger@linux-foundation.org>
next prev parent reply other threads:[~2007-05-29 15:10 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-05-29 9:18 [PATCH-2.4] Fix divide by 0 in vegas_cong_avoid() Lior Dotan
2007-05-29 15:05 ` Stephen Hemminger [this message]
2007-05-29 18:23 ` Lior Dotan
2007-05-29 22:02 ` Stephen Hemminger
2007-05-30 7:49 ` Ilpo Järvinen
2007-05-30 16:34 ` Stephen Hemminger
2007-05-30 18:56 ` Ilpo Järvinen
2007-05-29 20:22 ` Stephen Hemminger
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