From owner-freebsd-current  Fri Dec 20  0:22:58 2002
Delivered-To: freebsd-current@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id 8777237B401
	for <current@FreeBSD.ORG>; Fri, 20 Dec 2002 00:22:57 -0800 (PST)
Received: from mailman.zeta.org.au (mailman.zeta.org.au [203.26.10.16])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 5D7EF43EE6
	for <current@FreeBSD.ORG>; Fri, 20 Dec 2002 00:22:56 -0800 (PST)
	(envelope-from bde@zeta.org.au)
Received: from katana.zip.com.au (katana.zip.com.au [61.8.7.246])
	by mailman.zeta.org.au (8.9.3/8.8.7) with ESMTP id TAA24538;
	Fri, 20 Dec 2002 19:22:35 +1100
Date: Fri, 20 Dec 2002 19:24:15 +1100 (EST)
From: Bruce Evans <bde@zeta.org.au>
X-X-Sender: bde@gamplex.bde.org
To: Sean Kelly <smkelly@zombie.org>
Cc: current@FreeBSD.ORG
Subject: Re: `cat /dev/io` leads to system lockup.
In-Reply-To: <20021220062935.GA699@edgemaster.zombie.org>
Message-ID: <20021220190007.B344-100000@gamplex.bde.org>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Sender: owner-freebsd-current@FreeBSD.ORG
Precedence: bulk
List-ID: <freebsd-current.FreeBSD.ORG>
List-Archive: <http://docs.freebsd.org/mail/> (Web Archive)
List-Help: <mailto:majordomo@FreeBSD.ORG?subject=help> (List Instructions)
List-Subscribe: <mailto:majordomo@FreeBSD.ORG?subject=subscribe%20freebsd-current>
List-Unsubscribe: <mailto:majordomo@FreeBSD.ORG?subject=unsubscribe%20freebsd-current>
X-Loop: FreeBSD.ORG

On Fri, 20 Dec 2002, Sean Kelly wrote:

> On my 5.0-CURRENT kernel built 45 minutes ago, I can bring my system to its
> knees by doing
>
> # cat /dev/io
>
> While I understand that this isn't exactly something one would normally be
> doing, is it really something that should bring the system down?

No.  Writing to /dev/io is not supported.  write(2) to a device that
doesn't support writing should return -1 and set errno to ENODEV.

This was broken mainly by removing the default case from mem.c:mmrw().
This causes mmrw() to loop endlessly without giving up control.  Giant
locking in -current makes this especially fatal -- mmrw() holds Giant
so even most interrupt handlers are blocked.

In RELENG_4 the only bug near here is that mmrw() returns ENXIO instead
of ENODEV for writes to /dev/io.

Bruce


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