Subject: Re: oops in tcp_xmit_retransmit_queue() w/ v2.6.32.15

From: Lennart Schulte <[email-masked]>
Date: Mon, 19 Jul 2010 10:06:09 +0200

I ran tests for about 2 hours with this patch and I got no output from 
the debug patch. This seems to have solved at least my problem :)

Thanks!
> [PATCH] tcp: fix crash in tcp_xmit_retransmit_queue
>
> It can happen that there are no packets in queue while calling
> tcp_xmit_retransmit_queue(). tcp_write_queue_head() then returns
> NULL and that gets deref'ed to get sacked into a local var.
>
> There is no work to do if no packets are outstanding so we just
> exit early.
>
> There may still be another bug affecting this same function.
>
> Signed-off-by: Ilpo Järvinen<[email-masked]>
> Reported-by: Lennart Schulte<[email-masked]>
> ---
>   net/ipv4/tcp_output.c |    3 +++
>   1 files changed, 3 insertions(+), 0 deletions(-)
>
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index b4ed957..7ed9dc1 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -2208,6 +2208,9 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
>   	int mib_idx;
>   	int fwd_rexmitting = 0;
>
> +	if (!tp->packets_out)
> +		return;
> +
>   	if (!tp->lost_out)
>   		tp->retransmit_high = tp->snd_una;
>
>