From owner-freebsd-stable@freebsd.org  Thu Oct 13 14:38:36 2016
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Date: Thu, 13 Oct 2016 17:38:25 +0300
From: Slawa Olhovchenkov <slw@zxy.spb.ru>
To: Julien Charbon <jch@freebsd.org>
Cc: Konstantin Belousov <kostikbel@gmail.com>, freebsd-stable@FreeBSD.org,
 hiren panchasara <hiren@strugglingcoder.info>
Subject: Re: 11.0 stuck on high network load
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On Thu, Oct 13, 2016 at 01:56:21PM +0200, Julien Charbon wrote:

> >>  Something like:
> > 
> > Yes, thanks!
> 
>  Proposed changes added in the review:
> 
> https://reviews.freebsd.org/D8211
> 
>  tell me when you have three days without issue with this change.
> 
> >> tcp_detach() {
> >>
> >>   ...
> >>   if (inp->inp_flags & INP_TIMEWAIT) {
> >>
> >>     ...
> >>     if (inp->inp_flags & INP_DROPPED) {
> >>
> >>       in_pcbdetach(inp);
> >>       if (__predict_true(tp == NULL)) {
> >>           in_pcbfree(inp);
> >>       } else {
> >> #ifdef INVARIANTS
> >>         panic("tcp_detach: tp != NULL, That's not good because 'blah'\n");
> >> #else
> >>         log(LOG_ERR, "tcp_detach: tp != NULL, That's not good because
> >> 'blah'\n");
> > 
> > May be some more info in log can help to detect root cause of issuse?
> > I am don't know what info, may be flags or number of references?
> 
>  For this kind of issue, the useful part is the stacktrace.  INVARIANT

Like this?

#ifdef KDB
                kdb_backtrace();
#endif

as found in sys/netgraph/ng_base.c

> will give you that trace in the core, and without INVARIANT then it is
> better to use dtrace:
> 
> $ cat tcp-twstart-dropped.d
> fbt::tcp_twstart:entry
> /args[0]->t_inpcb->inp_flags & 0x04000000/
> {
>   stack();
>   printf("INP_DROPPED in tcp_twstart: %x", args[0]->t_inpcb->inp_flags);
> }

Same code may be insert there too, IMHO.

> --
> Julien
> 
>