From owner-freebsd-stable@freebsd.org  Wed Feb 15 15:18:01 2017
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Subject: Re: net.inet.udp.log_in_vain strange syslog reports
To: Mark Martinec <Mark.Martinec+freebsd@ijs.si>, freebsd-stable@freebsd.org
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From: Eric van Gyzen <vangyzen@FreeBSD.org>
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Date: Wed, 15 Feb 2017 09:17:54 -0600
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On 02/15/2017 08:56, Mark Martinec wrote:
> In a similar vein, I noticed also the following in our logs,
> with net.inet.tcp.log_in_vain=1.
>
> Looks like messages got concatenated somehow:
>
> Jan 25 01:37:53 mildred kernel: TCP: [2607:ff10:c5:509a::10]:26459 to
> [2001:1470:ff80::80:16]:4911 tcpflags 0x2<SYN>; tcp_input: Connection attempt to
> closed TCP: [2607:ff10:c5:509a::10]:14898 to [2001:1470:ff80::80:16]:5222
> tcpflags 0x2<SYN>; tcp_input: Connection attempt to closed port

The length of the truncated "TCP:...closed" message is just under 128, which is 
the PRINTF_BUFR_SIZE as defined in sys/amd64/conf/GENERIC.  You could try 
increasing this value and rebuilding your kernel to see if that fixes the 
truncation.  Don't increase it very much, since it's used to declare a buffer on 
the stack, and stack space is quite limited.  For this case, 180 should be enough.

Eric