From owner-freebsd-fs@freebsd.org  Fri Oct 14 10:23:05 2016
Return-Path: <owner-freebsd-fs@freebsd.org>
Delivered-To: freebsd-fs@mailman.ysv.freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 by mailman.ysv.freebsd.org (Postfix) with ESMTP id A3BABC11126
 for <freebsd-fs@mailman.ysv.freebsd.org>; Fri, 14 Oct 2016 10:23:05 +0000 (UTC)
 (envelope-from julian@freebsd.org)
Received: from vps1.elischer.org (vps1.elischer.org [204.109.63.16])
 (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
 (Client CN "vps1.elischer.org",
 Issuer "CA Cert Signing Authority" (not verified))
 by mx1.freebsd.org (Postfix) with ESMTPS id 833CB813
 for <freebsd-fs@FreeBSD.org>; Fri, 14 Oct 2016 10:23:04 +0000 (UTC)
 (envelope-from julian@freebsd.org)
Received: from julian-mbp3.pixel8networks.com
 (50-196-156-133-static.hfc.comcastbusiness.net [50.196.156.133])
 (authenticated bits=0)
 by vps1.elischer.org (8.15.2/8.15.2) with ESMTPSA id u9EAN26T096040
 (version=TLSv1.2 cipher=DHE-RSA-AES128-SHA bits=128 verify=NO)
 for <freebsd-fs@FreeBSD.org>; Fri, 14 Oct 2016 03:23:03 -0700 (PDT)
 (envelope-from julian@freebsd.org)
To: "freebsd-fs@freebsd.org" <freebsd-fs@FreeBSD.org>
From: Julian Elischer <julian@freebsd.org>
Subject: oddness in 10,3 .. mnt_ref leak?
Message-ID: <58942da1-0b65-2b34-d91b-2fafcfa7d86b@freebsd.org>
Date: Fri, 14 Oct 2016 03:22:57 -0700
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:45.0)
 Gecko/20100101 Thunderbird/45.4.0
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
X-BeenThere: freebsd-fs@freebsd.org
X-Mailman-Version: 2.1.23
Precedence: list
List-Id: Filesystems <freebsd-fs.freebsd.org>
List-Unsubscribe: <https://lists.freebsd.org/mailman/options/freebsd-fs>,
 <mailto:freebsd-fs-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-fs/>
List-Post: <mailto:freebsd-fs@freebsd.org>
List-Help: <mailto:freebsd-fs-request@freebsd.org?subject=help>
List-Subscribe: <https://lists.freebsd.org/mailman/listinfo/freebsd-fs>,
 <mailto:freebsd-fs-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 14 Oct 2016 10:23:05 -0000

I'm runnign 10.3 in our appliance and by chance I added code to print 
out the mnt-ref values of struct mount as htey are being changed..

to my surprise that reference count seems to be wildly wrong..

I added the following code to be run when it is decremented:

#define MNT_REL(mp)     do {                                            \
         if ((mp)->mnt_ref > 0) {                                        \
(mp)->mnt_ref--;                                        \
         } else {                                                        \
                 printf("### %s (%s) negative mnt_ref, %d\n", __func__ 
,mp->mnt_stat.f_mntonname, mp->mnt_ref);  \
                 (mp->mnt_ref = 0);                                      \
} \
         if ((mp)->mnt_ref == 0)                                         \
wakeup((mp));                                           \
} while (0)

and I see this every few seconds:

### vfs_unbusy (/opt/pixel8/master_config) negative mnt_ref, 0


is there a chance that vfs_unbusy has no balancing MNT_REF when the 
file system becomes active again?

I've looked through our patches (we do have some)  but don't see a 
reason for this in them.


Julian