From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by ozlabs.org (Postfix) with ESMTP id 6D2E8B6F71 for ; Wed, 20 Apr 2011 22:33:41 +1000 (EST) Date: Wed, 20 Apr 2011 18:03:30 +0530 From: Amit Shah To: Milton Miller 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 In-Reply-To: Cc: linuxppc-dev@ozlabs.org, Rusty Russell , linux-kernel@vger.kernel.org, greg@kroah.com List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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