From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758346Ab2AEVBq (ORCPT ); Thu, 5 Jan 2012 16:01:46 -0500 Received: from mx1.redhat.com ([209.132.183.28]:1765 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758265Ab2AEVBp (ORCPT ); Thu, 5 Jan 2012 16:01:45 -0500 Date: Thu, 5 Jan 2012 16:01:23 -0500 From: Don Zickus To: Seiji Aguchi Cc: "Luck, Tony" , "linux-kernel@vger.kernel.org" , Matthew Garrett , Vivek Goyal , "Chen, Gong" , "akpm@linux-foundation.org" , "Brown, Len" , "'ying.huang@intel.com'" <'ying.huang@intel.com'>, "'ak@linux.intel.com'" <'ak@linux.intel.com'>, "'hughd@chromium.org'" <'hughd@chromium.org'>, "'mingo@elte.hu'" <'mingo@elte.hu'>, "jmorris@namei.org" , "a.p.zijlstra@chello.nl" , "namhyung@gmail.com" , "dle-develop@lists.sourceforge.net" , Satoru Moriya Subject: Re: [RFC][PATCH v4 -next 1/4] Move kmsg_dump(KMSG_DUMP_PANIC) below smp_send_stop() Message-ID: <20120105210123.GI5650@redhat.com> References: <5C4C569E8A4B9B42A84A977CF070A35B2C5827AF7F@USINDEVS01.corp.hds.com> <5C4C569E8A4B9B42A84A977CF070A35B2C5827AF81@USINDEVS01.corp.hds.com> <3908561D78D1C84285E8C5FCA982C28FBB21@ORSMSX104.amr.corp.intel.com> <5C4C569E8A4B9B42A84A977CF070A35B2C5827B01D@USINDEVS01.corp.hds.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5C4C569E8A4B9B42A84A977CF070A35B2C5827B01D@USINDEVS01.corp.hds.com> 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 On Thu, Jan 05, 2012 at 03:10:25PM -0500, Seiji Aguchi wrote: > > >Aren't you worried about the comment about smp_send_stop() not > >being hardened to work in a panic situation? > > /* > > * Note smp_send_stop is the usual smp shutdown function, which > > * unfortunately means it may not be hardened to work in a panic > > This comment is wrong because Don improved smp_send_stop() by switching REBOOT_VECTOR to NMI. > And his patch has already merged to linux-next tree. I only fixed x86. Who knows what the other arches do.. I don't know how to prove something is hardened other than not seeing any hangs or false reboots on in that piece of code. Cheers, Don > > http://git.kernel.org/?p=linux/kernel/git/next/linux-next.git;a=commitdiff;h=3603a2512f9e69dc87914ba922eb4a0812b21cd6 > > So, current smp_send_stop() is hardened to work in a panic situation. > > I will remove this wrong comment. > > Seiji > > >-----Original Message----- > >From: Luck, Tony [mailto:tony.luck@intel.com] > >Sent: Thursday, January 05, 2012 2:07 PM > >To: Seiji Aguchi; Don Zickus > >Cc: linux-kernel@vger.kernel.org; Matthew Garrett; Vivek Goyal; Chen, Gong; akpm@linux-foundation.org; Brown, Len; > >'ying.huang@intel.com'; 'ak@linux.intel.com'; 'hughd@chromium.org'; 'mingo@elte.hu'; jmorris@namei.org; > >a.p.zijlstra@chello.nl; namhyung@gmail.com; dle-develop@lists.sourceforge.net; Satoru Moriya > >Subject: RE: [RFC][PATCH v4 -next 1/4] Move kmsg_dump(KMSG_DUMP_PANIC) below smp_send_stop() > > > >- kmsg_dump(KMSG_DUMP_PANIC); > >- > > /* > > * Note smp_send_stop is the usual smp shutdown function, which > > * unfortunately means it may not be hardened to work in a panic > >@@ -117,6 +115,8 @@ void panic(const char *fmt, ...) > > */ > > smp_send_stop(); > > > >+ kmsg_dump(KMSG_DUMP_PANIC); > >+ > > > >Aren't you worried about the comment about smp_send_stop() not > >being hardened to work in a panic situation? > > > >If it does work - we are clearly much better off moving the > >kmsg_dump() call down like this. It makes life much simpler > >and cleaner to work with just one running cpu. > > > >But if something goes wrong - we might not see the dump at all! > > > >How do we compare these cases and decide that it is better to > >trust that smp_send_stop() will return? > > > >-Tony