Date: Mon, 29 Dec 2014 23:51:08 +0000 From: "Bjoern A. Zeeb" <bzeeb-lists@lists.zabbadoz.net> To: Nikolay Denev <ndenev@gmail.com> Cc: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org> Subject: Re: setfib and RSTs Message-ID: <81C17F4A-B0AA-48C9-ABFB-6B14B7223643@lists.zabbadoz.net> In-Reply-To: <CA%2BP_MZGa8s9PzhoA=kY8YRcG5kRsVb=oP8pjtOXV%2BDH_meG2nQ@mail.gmail.com> References: <CA%2BP_MZHi1hMGq8qbOvpYSMLk4Usr4CAXjR1PdKRt7dE_vMJ7UQ@mail.gmail.com> <54A0FDD9.4090009@freebsd.org> <CA%2BP_MZGsX3_UB2wigrD-WWB0aN=bSf9Xxw147y2vWLAJ6_syng@mail.gmail.com> <CAJ-Vmo=B3c9p6nMpHA6z75oKBErTrX0Ru8MDhHw1MgN=Ts_%2B_w@mail.gmail.com> <CA%2BP_MZGa8s9PzhoA=kY8YRcG5kRsVb=oP8pjtOXV%2BDH_meG2nQ@mail.gmail.com>
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> On 29 Dec 2014, at 21:03 , Nikolay Denev <ndenev@gmail.com> wrote:
>
> No, no PR yet, but I will file one. I wanted to collect some more data
> first.
>
> So, I've did some dtrace digging :
>
> [20:54][root@nas:~]#cat reset.d
> #!/usr/sbin/dtrace -s
>
> fbt:kernel:tcp_dropwithreset:entry
> {
> printf("reason %d fib %d src_port %d dst_port %d", args[4], args[2] ?
> args[2]->t_inpcb->inp_inc.inc_fibnum : -1, ntohs(args[1]->th_sport),
> ntohs(args[1]->th_dport));
> /* stack(); */
> }
> …
> The port numbers here match RST packets that I'm seeing with tcpdump in
> another window.
> reason 3 is BANDLIM_RST_CLOSEDPORT (from icmp_var.h)
> Looking at tcp_input.c I see that there are cases where the INPCB does not
> exists, and from what I see this is how the FIB gets determined.
> Also here I see that tcp_dropwithreset() is called with tcpcb set to NULL,
> so probably this is why the FIB is not found.
>
> Why this is happening, I have no idea yet.
Could you also check for the mbuf *m and the fibnum from the pkthdr there?
It might be even more interesting to see this for tcp_respond and the following ip_output as well, in case you want to keep state in the d script; otherwise just tcp_dropwithreset and/or tcp_respond should be fine.
Usually I would expect for the tcp_dropwithreset case that inp will be NULL in tcp_respond, the mbuf *m and th will be valid and thus the FIB number from the incoming mbuf would be re-used as the mbuf will be re-used, but for that the mbuf needs to be properly tagged on receive.
/bz
—
Bjoern A. Zeeb Charles Haddon Spurgeon:
"Friendship is one of the sweetest joys of life. Many might have failed
beneath the bitterness of their trial had they not found a friend."
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