From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760075AbXHGHZh (ORCPT ); Tue, 7 Aug 2007 03:25:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754929AbXHGHZ2 (ORCPT ); Tue, 7 Aug 2007 03:25:28 -0400 Received: from smtp2.linux-foundation.org ([207.189.120.14]:56316 "EHLO smtp2.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753822AbXHGHZ1 (ORCPT ); Tue, 7 Aug 2007 03:25:27 -0400 Date: Tue, 7 Aug 2007 00:24:37 -0700 From: Andrew Morton To: Greg KH Cc: "Denis V. Lunev" , "Denis V. Lunev" , dev@openvz.org, devel@openvz.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] pci_get_device call from interrupt in reboot fixups Message-Id: <20070807002437.0e7b9ee5.akpm@linux-foundation.org> In-Reply-To: <20070807024910.GB13657@suse.de> References: <20070803103924.GA23786@iris.sw.ru> <20070804040806.GF23330@suse.de> <46B6CAC4.3080202@sw.ru> <20070807024910.GB13657@suse.de> X-Mailer: Sylpheed 2.4.1 (GTK+ 2.8.17; x86_64-unknown-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 6 Aug 2007 19:49:10 -0700 Greg KH wrote: > On Mon, Aug 06, 2007 at 11:16:20AM +0400, Denis V. Lunev wrote: > > Greg KH wrote: > > > On Fri, Aug 03, 2007 at 02:39:24PM +0400, Denis V. Lunev wrote: > > >> The following calltrace is possible now: > > >> handle_sysrq > > >> machine_emergency_restart > > >> mach_reboot_fixups > > >> pci_get_device > > >> pci_get_subsys > > >> down_read > > >> The patch obtains PCI device during initialization to avoid bothering PCI > > >> search engine in interrupt. Devices used in this code are not supposed to > > >> be pluggable, so it looks safe to keep them. > > > > > > What devices are supposed to be affected here? Are you sure that they > > > can't be removed later? Grabbing references here might mess with them > > > in the future. > > Right now the list is the following: > > static struct device_fixup fixups_table[] = { > > { PCI_VENDOR_ID_CYRIX, PCI_DEVICE_ID_CYRIX_5530_LEGACY, > > cs5530a_warm_reset }, > > { PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_CS5536_ISA, cs5536_warm_reset }, > > }; > > > > Though, if the approach is not suitable, we can skip fixups if we came > > from sysrq. > > I don't think we really need to do fixups when we are "crashing" like > this. The user really isn't shutting down the kernel as it should > normally do. > > Andrew, I really don't want to change the PCI core to handle this, as we > finally fixed a lot of issues with drivers trying to walk these lists > from interrupt context. So if you want to just hide the warning message > as we are shutting down, that's fine with me. Or just don't do the > fixups. But grabbing a reference to the pci device is unsafe in my > opinion and I do not want to do that. > OK, good decision ;) One approach would be for some brave soul to pick his way through the reboot code and ensure that we are correctly and reliably setting system_state to SYSTEM_RESTART, then test that in __might_sleep(). But this does suppress somewhat-useful debugging just because of sysrq-B and I really wouldn't want to utilise the horrid system_state any more that we are presently doing. I think on balance that it would be better if we could do something more targetted, like modify emergency_restart() to test in_interrupt() and to then apologetically set some well-named global flag which will shut up __might_sleep(). Pretty foul, but I can't think of anything better.