Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754733Ab1DTMdp (ORCPT ); Wed, 20 Apr 2011 08:33:45 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41041 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752471Ab1DTMdo (ORCPT ); Wed, 20 Apr 2011 08:33:44 -0400 Date: Wed, 20 Apr 2011 18:03:30 +0530 From: Amit Shah To: Milton Miller Cc: Rusty Russell , linux-kernel@vger.kernel.org, benh@kernel.crashing.org, greg@kroah.com, linuxppc-dev@ozlabs.org Subject: Re: hvc_console: Don't access hvc_task if not initialised Message-ID: <20110420123330.GB3519@amit-x200.redhat.com> References: <20110325084714.GA28356@amit-x200.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1409 Lines: 39 On (Mon) 28 Mar 2011 [11:52:05], Milton Miller wrote: > On Fri, 25 Mar 2011 about 14:17:14 +0530, Amit Shah wrote: > > On (Thu) 24 Mar 2011 [08:58:04], Milton Miller wrote: > > > On Thu, 24 Mar 2011 07:29:58 -0000, Amit Shah wrote: > > > > hvc_open() can be called without having any backing device. This > > > > results in a call to hvc_kick() which calls wake_up_process on a NULL > > > > pointer. > > > > > > How is hvc_open called without a hvc_driver registered to the tty layer? > > > > This gets reproduced in a couple of scenarios, I'm trying to get more > > information. OK - I finally could reproduce myself, albiet it's a panic in hvc_open, not the one mentioned earlier. hvc_console is built into the kernel and virtio_console is a module. This sequence triggers a panic: - modprobe virtio_console - agetty /dev/hvc0 9600 vt100 - rmmod virtio_console - modprobe virtio_console - agetty /dev/hvc0 9600 vt100 A patch that I had sent previously, to hvc_remove() a port when the associated virtio_console port gets unplugged, fixes this panic. Stricter checking in hvc_open(), as you mentioned, will solve the other one as well. Thanks! Amit -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/