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Date: Tue, 16 Feb 2016 00:44:46 +0300
From: Slawa Olhovchenkov <slw@zxy.spb.ru>
To: Giuseppe Lettieri <g.lettieri@iet.unipi.it>
Cc: Luigi Rizzo <rizzo@iet.unipi.it>, Adrian Chadd <adrian.chadd@gmail.com>,
 "stable@freebsd.org" <stable@freebsd.org>
Subject: Re: 82576 + NETMAP + VLAN
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On Mon, Feb 15, 2016 at 05:02:36PM +0100, Giuseppe Lettieri wrote:

> Il 15/02/2016 16:13, Slawa Olhovchenkov ha scritto:
> > On Mon, Feb 15, 2016 at 04:10:30PM +0100, Giuseppe Lettieri wrote:
> >
> >> Hi Slawa,
> >>
> >> I think WITNESS is seeing a false positive, since those two are always
> >> different mutexes.
> >>
> >> The actual deadlock you experience should be caused by something else. I
> >
> > Are you sure? When deadlock occur I am see threads waiting on nm_kn_lock.
> 
> The deadlock I mentioned still involves nm_kn_locks, sorry if I was not 
> clear about that. I am just saying that we never try to take the same 
> lock that we already holding.
> 
> Nonetheless, there are indeed problems in the path that WITNESS has 
> seen. The problem is that pipes have to notify the other end while 
> called by kevent. kevent holds the nm_kn_lock on the TX src ring and the 
> notification takes the nm_kn_lock on the RX dst ring.

Can you comment other issuses? Is this by design or is this bug?

- with kevent sync for transmiting need first register
  EVFILT_WRITE/EV_DISABLE and after every write
  EVFILT_WRITE/EV_DISPATCH

- with kevent sync all opening /dev/netmap and registering need do
  from same thread as kevent using for sinc (unless no RX/TX).