netdev - Re: [PATCH] sctp: make the max

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Message-ID: <20131202115640.GA10857@hmsreliant.think-freely.org>
Date:	Mon, 2 Dec 2013 06:56:40 -0500
From:	Neil Horman <nhorman@...driver.com>
To:	Wang Weidong <wangweidong1@...wei.com>
Cc:	Vlad Yasevich <vyasevich@...il.com>,
	David Miller <davem@...emloft.net>, linux-sctp@...r.kernel.org,
	netdev@...r.kernel.org, dingtianhong@...wei.com
Subject: Re: [PATCH] sctp: make the max_burst min value to 1

On Mon, Dec 02, 2013 at 02:51:45PM +0800, Wang Weidong wrote:
> From: Wang Weidong <wangweidong1@...wei.com>
> 
> when I setted the max_burst to 0, do the lksctp-tools I got hang.
> I found sctp_transport_burst_limited would make the cwnd to 0.
> so I make the max_burst min value to 1.
> Signed-off-by: Wang Weidong <wangweidong1@...wei.com>
> ---
>  net/sctp/sysctl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/sctp/sysctl.c b/net/sctp/sysctl.c
> index 7637e8e..46832d3 100644
> --- a/net/sctp/sysctl.c
> +++ b/net/sctp/sysctl.c
> @@ -135,7 +135,7 @@ static struct ctl_table sctp_net_table[] = {
>  		.maxlen		= sizeof(int),
>  		.mode		= 0644,
>  		.proc_handler	= proc_dointvec_minmax,
> -		.extra1		= &zero,
> +		.extra1		= &one,
>  		.extra2		= &int_max
>  	},
>  	{
> -- 
> 1.7.12
> 
> 


This seems like a band-aid to me.  There are a few things wrong:

1) You can also set the the max_burst via setsockopt, and so this would need to
be checked in that path as well.

2) I don't see how having a cwnd of zero would cause a hang.  It looks like a
cwnd of zero would perpetually place the association in a slow start state,
which is silly but not illegal.  

Please investigate the acutally root cause of the problem before just avoiding
it like this.

Thanks!
Neil

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