From owner-freebsd-current@FreeBSD.ORG  Fri Jan 18 05:45:49 2013
Return-Path: <owner-freebsd-current@FreeBSD.ORG>
Delivered-To: freebsd-current@FreeBSD.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 by hub.freebsd.org (Postfix) with ESMTP id 69D1BECC
 for <freebsd-current@FreeBSD.org>; Fri, 18 Jan 2013 05:45:49 +0000 (UTC)
 (envelope-from okuno.kohji@jp.panasonic.com)
Received: from smtp.mei.co.jp (smtp.mei.co.jp [133.183.100.20])
 by mx1.freebsd.org (Postfix) with ESMTP id E6780E2C
 for <freebsd-current@FreeBSD.org>; Fri, 18 Jan 2013 05:45:48 +0000 (UTC)
Received: from mail-gw.jp.panasonic.com ([157.8.1.157])
 by smtp.mei.co.jp (8.12.11.20060614/3.7W/kc-maile13) with ESMTP id
 r0I5jlOs017896
 for <freebsd-current@FreeBSD.org>; Fri, 18 Jan 2013 14:45:47 +0900 (JST)
Received: from epochmail.jp.panasonic.com ([157.8.1.130])
 by mail.jp.panasonic.com (8.11.6p2/3.7W/kc-maili11) with ESMTP id r0I5jka16587
 for <freebsd-current@FreeBSD.org>; Fri, 18 Jan 2013 14:45:46 +0900
Received: by epochmail.jp.panasonic.com (8.12.11.20060308/3.7W/lomi17) id
 r0I5jkwN024042; Fri, 18 Jan 2013 14:45:46 +0900
Received: from localhost
 by lomi17.jp.panasonic.com (8.12.11.20060308/3.7W) with ESMTP id
 r0I5jksA024022; Fri, 18 Jan 2013 14:45:46 +0900
Date: Fri, 18 Jan 2013 14:45:38 +0900 (JST)
Message-Id: <20130118.144538.1860198911942517633.okuno.kohji@jp.panasonic.com>
To: freebsd-current@FreeBSD.org
Subject: deadlock between g_event and a thread on removing a device.
From: Kohji Okuno <okuno.kohji@jp.panasonic.com>
Organization: Panasonic Corporation
X-Mailer: Mew version 6.5 on Emacs 23.4 / Mule 6.0 (HANACHIRUSATO)
Mime-Version: 1.0
Content-Type: Text/Plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Cc: okuno.kohji@jp.panasonic.com
X-BeenThere: freebsd-current@freebsd.org
X-Mailman-Version: 2.1.14
Precedence: list
List-Id: Discussions about the use of FreeBSD-current
 <freebsd-current.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/options/freebsd-current>, 
 <mailto:freebsd-current-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-current>
List-Post: <mailto:freebsd-current@freebsd.org>
List-Help: <mailto:freebsd-current-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>,
 <mailto:freebsd-current-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 18 Jan 2013 05:45:49 -0000

Hi,

When I removed a device (ex. /dev/da0), I have encounterd a
dead-lock between ``g_event'' thread and a thread that is opening
device file (I call this thread as A).

Would you refer the following?

When the device is removed between dev_refthread() and g_dev_open(),
thread A incremented dev->si_threadcount, but can't acquire
topology_lock.

On the other hand, g_event is waiting to set dev->si_threadcount to 0
with topology_lock.

Regards,
 Kohji Okuno


<<< Thread A >>>
...
devfs_open()
{
  ...
  dsw = dev_refthread(dev, &ref); <= increment dev->si_threadcount
  ...
  error = dsw->d_open(...);       <= call g_dev_open()
  ...
  dev_relthread(dev, ref);        <= decrement dev->si_threadcount
}

g_dev_open()
{
  ...
  g_topology_lock();              <= Thread A couldn't acquire 
  ...                                topology_lock.
}

<<< g_event >>>
g_run_events()
{
   ...
   g_topology_lock();             <= g_event acuired topology_lock here.
   ...
   one_event()
   ...
}

one_event()
g_orphan_register()
g_dev_orphan()
destroy_dev()
destroy_dev()
destroy_devl()
{
  ...
  while (dev->si_threadcount != 0) { <= this count was incremented by Thread A
    /* Use unique dummy wait ident */
    msleep(&csw, &devmtx, PRIBIO, "devdrn", hz / 10);
  }
  ...
}