From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753511AbYGaNZq (ORCPT ); Thu, 31 Jul 2008 09:25:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751160AbYGaNZh (ORCPT ); Thu, 31 Jul 2008 09:25:37 -0400 Received: from ecfrec.frec.bull.fr ([129.183.4.8]:51244 "EHLO ecfrec.frec.bull.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751101AbYGaNZg convert rfc822-to-8bit (ORCPT ); Thu, 31 Jul 2008 09:25:36 -0400 Date: Thu, 31 Jul 2008 15:26:06 +0200 From: Sebastien Dugue To: michael@ellerman.id.au Cc: linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, benh@kernel.crashing.org, paulus@samba.org, jean-pierre.dion@bull.net, gilles.carry@ext.bull.net, tinytim@us.ibm.com, tglx@linutronix.de, rostedt@goodmis.org Subject: Re: [PATCH] powerpc - Initialize the irq radix tree earlier Message-ID: <20080731152606.5ae7c379@bull.net> In-Reply-To: <1217509299.19050.15.camel@localhost> References: <1217497241-10685-1-git-send-email-sebastien.dugue@bull.net> <1217497241-10685-2-git-send-email-sebastien.dugue@bull.net> <1217504456.9817.22.camel@localhost> <20080731140002.31bbe4a0@bull.net> <1217509104.19050.11.camel@localhost> <1217509299.19050.15.camel@localhost> X-Mailer: Claws Mail 3.2.0 (GTK+ 2.12.2; i486-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 31 Jul 2008 23:01:39 +1000 Michael Ellerman wrote: > On Thu, 2008-07-31 at 22:58 +1000, Michael Ellerman wrote: > > On Thu, 2008-07-31 at 14:00 +0200, Sebastien Dugue wrote: > > > On Thu, 31 Jul 2008 21:40:56 +1000 Michael Ellerman wrote: > > > > > > > > This boot ordering stuff is pretty hairy, so I might have missed > > > > something, but this is how the code is ordered AFAICT: > > > >  > > > > start_kernel() > > > > init_IRQ() > > > > ... > > > > local_irq_enable() > > > > ... > > > > rest_init() > > > > kernel_thread() > > > > kernel_init() > > > > smp_prepare_cpus() > > > > smp_xics_probe() (via smp_ops->probe()) > > > > > > > > > > > > What's stopping us from taking an irq between local_irq_enable() and > > > > smp_xics_probe() ? Is it just that no one's request_irq()'ed them yet? > > > > > > It's hairy, I agree, but as you've mentioned no one has done a request_irq() > > > at that point. The first one to do it is smp_xics_probe() for the IPI. > > > > Hmm, I don't think that's strong enough. I can trivially cause irqs to > > fire during a kexec reboot just by mashing the keyboard. > > > > And during a kdump boot all sorts of stuff could be firing. Even during > > a clean boot, from firmware, I don't think we can guarantee that > > nothing's going to fire. > > > > .. after a bit of testing .. > > > > It seems it actually works (sort of). > > > > xics_remap_irq() calls irq_radix_revmap_lookup(), which calls: > > > > ptr = radix_tree_lookup(&host->revmap_data.tree, hwirq); > > > > And because host->revmap_data.tree was zalloc'ed we trip on the first > > check here: > > @#$% ctrl-enter == send! > > Continuing ... > > void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index) > { > unsigned int height, shift; > struct radix_tree_node *node, **slot; > > node = rcu_dereference(root->rnode); > if (node == NULL) > return NULL; > > Which means irq_radix_revmap_lookup() will return NO_IRQ, which is cool. Which is what I intended so that as long as no IRQ is registered we return NO_IRQ. > > > So I think it can fly, as long as we're happy that we can't reverse map > anything until smp_xics_probe() - and I think that's true, as any irq we > take will be invalid. That's true as no IRQs are registered before smp_xics_probe() and for any interrupt we might get before that, irq_radix_revmap_lookup() will return NO_IRQ. Thanks, Sebastien.