From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751033Ab2BHULw (ORCPT ); Wed, 8 Feb 2012 15:11:52 -0500 Received: from mx1.redhat.com ([209.132.183.28]:25585 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750716Ab2BHULv (ORCPT ); Wed, 8 Feb 2012 15:11:51 -0500 Date: Wed, 8 Feb 2012 15:11:45 -0500 From: Don Zickus To: "Eric W. Biederman" Cc: Vivek Goyal , x86@kernel.org, LKML , kexec-list Subject: Re: [PATCH] x86, kdump: No need to disable ioapic in crash path Message-ID: <20120208201145.GX5650@redhat.com> References: <1328206323-25580-1-git-send-email-dzickus@redhat.com> <20120207215741.GD5650@redhat.com> <20120207221924.GH6346@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 On Tue, Feb 07, 2012 at 03:35:59PM -0800, Eric W. Biederman wrote: > Vivek Goyal writes: > > > On Tue, Feb 07, 2012 at 04:57:41PM -0500, Don Zickus wrote: > >> On Thu, Feb 02, 2012 at 03:24:46PM -0800, Eric W. Biederman wrote: > >> > > Eric, brought up a point that because the boot code was restructured we may > >> > > not need to disable the io apic any more in the crash path. The original > >> > > concern that led to the development of disable_IO_APIC, was that the TSC > >> > > calibration on boot up relied on the PIT timer for reference. Access > >> > > to the PIT required 8259 interrupts to be working. This wouldn't work > >> > > if the ioapic needed to be configured. So on panic path, the ioapic was > >> > > reconfigured to use virtual wire mode to allow the 8259 to passthrough. > >> > > >> > A small clarification originally it was the jiffies calibration that > >> > would fail if we could cause the PIT to generate interrupts through the > >> > 8259. The boot would then hang at calibrating jiffies. > >> > >> Ok. Thanks! > > > > So now what has changed? Do we setup LAPIC and IOAPIC early enough to > > receive PIT interrupts in regular mode (non-virtual wire mode) or > > something else? > > Yes. Part of the Moorstown work required that this be done because > moorsetown did not support legacy mode. Last I looked the code hadn't > been generalized beyond Moorsetown but empirically it works now. > > Don as to what to test the only case I can think of that might be spooky > is a screaming interrupt during the handover. You might want to try > playing with lkcdtm to try some of the more exotic crash scenarios. But > all I expect further testing might reveal are places where we are not > as robust in initializing the hardware as we might be. Things that > might have been papered over by the ioapic shutdown. I ran lkdtm by panic'ing in the interrupt handle thus leaving device interrupt un-ack'd and the apic might have been un-ack'd too (jprobes hooked in at do_IRQ). 3 out 3 times the second kernel came up on my core2 quad. Cheers, Don