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Date: Sun, 10 Mar 2019 12:26:29 +0200
From: Konstantin Belousov <kostikbel@gmail.com>
To: Hans Petter Selasky <hps@selasky.org>
Cc: Warner Losh <imp@bsdimp.com>,
 FreeBSD Hackers <freebsd-hackers@freebsd.org>,
 "O'Connor, Daniel" <darius@dons.net.au>
Subject: Re: USB stack getting confused
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On Sun, Mar 10, 2019 at 11:18:36AM +0100, Hans Petter Selasky wrote:
> On 3/10/19 10:47 AM, Konstantin Belousov wrote:
> >> Yes, I can do that if destroy_dev() ensures that d_close is called for
> >> all open file handles once and only once before it returns. I think this
> >> is where the problem comes from.
> > See above.  For d_close it is impossible, for cdevpriv dtr it is already
> > there by design.
> > 
> 
> Yes, cdevpriv_dtr will wait for the final close() from user-space 
> unfortunately. Or am I mistaken?

You are mistaken.  Cdevpriv destructors are called either on the file close
(not the last close in d_close sense, just file close) OR during destroy_dev().
Each destructor/file pair is called exactly once, regardless of the cause.