From owner-freebsd-bugs  Thu Mar 18 10:30:23 1999
Delivered-To: freebsd-bugs@freebsd.org
Received: from freefall.freebsd.org (freefall.FreeBSD.ORG [204.216.27.21])
	by hub.freebsd.org (Postfix) with ESMTP id 742B314DBF
	for <freebsd-bugs@FreeBSD.org>; Thu, 18 Mar 1999 10:30:19 -0800 (PST)
	(envelope-from gnats@FreeBSD.org)
Received: (from gnats@localhost)
	by freefall.freebsd.org (8.9.2/8.9.2) id KAA67070;
	Thu, 18 Mar 1999 10:30:00 -0800 (PST)
	(envelope-from gnats@FreeBSD.org)
Received: by hub.freebsd.org (Postfix, from userid 32767)
	id 7085D1550A; Thu, 18 Mar 1999 10:21:27 -0800 (PST)
Message-Id: <19990318182127.7085D1550A@hub.freebsd.org>
Date: Thu, 18 Mar 1999 10:21:27 -0800 (PST)
From: M.Indlekofer@fz-juelich.de
To: freebsd-gnats-submit@freebsd.org
X-Send-Pr-Version: www-1.0
Subject: kern/10653: cdevsw_module_handler MOD_UNLOAD problem
Sender: owner-freebsd-bugs@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.org


>Number:         10653
>Category:       kern
>Synopsis:       cdevsw_module_handler MOD_UNLOAD problem
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Thu Mar 18 10:30:00 PST 1999
>Closed-Date:
>Last-Modified:
>Originator:     Michael Indlekofer
>Release:        3.1-RELEASE
>Organization:
Forschungs Zentrum Juelich GmbH
>Environment:
FreeBSD control10... 3.1-RELEASE FreeBSD 3.1-RELEASE #0: Tue Mar 16
13:31:56 GMT 1999 root@control10.../usr/src/sys/compile/MYKERNEL.3 i386
>Description:
A char device driver which uses 
CDEV_MODULE(xxx_mod,MYMAJOR,xxx_devsw,xxx_handler,0)
and wants to prevent an unloading of the module
(because some devices he offers are still in use e.g.) has a problem:
kldunload -> /sys/kern/kern_conf.c:cdevsw_module_handler
which calls for MOD_UNLOAD the function cdevsw_add(...,NULL,NULL)
which unregisters our xxx_devsw! AFTERWARDS xxx_handler is asked
if he wants to unload,...but it's too late...the xxx_devsw is gone,
even for the case we don't want to unload!

In my case: A program used a device and kldunload was called.
xxx_handler returned EBUSY and kldunload said: can't unload, device busy.
The next time the program issued a ioctl for the still open device
the system crashed in spec_ioctl (gdb -k ...) with an invalid
entry in the cdevsw for MYMAJOR: Fatal trap 12: page fault in kernel mode.
>How-To-Repeat:
see example above
>Fix:
/sys/kern/kern_conf.c:???devsw_module_handler should consult the
module handler (data->chainevh) FIRST in the case of MOD_UNLOAD
whether the module want's to unload before it "kills" the devsw!

>Release-Note:
>Audit-Trail:
>Unformatted:


To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-bugs" in the body of the message