Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752000AbcCLJVj (ORCPT ); Sat, 12 Mar 2016 04:21:39 -0500 Received: from www.linutronix.de ([62.245.132.108]:40629 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750954AbcCLJV3 (ORCPT ); Sat, 12 Mar 2016 04:21:29 -0500 Date: Sat, 12 Mar 2016 10:19:57 +0100 (CET) From: Thomas Gleixner To: Boris Ostrovsky cc: Yanmin Zhang , Joerg Roedel , Peter Zijlstra , LKML , xiao jin , Peter Anvin , xen-devel , Borislav Petkov , Ingo Molnar Subject: Re: [Xen-devel] [patch 1/4] hotplug: Prevent alloc/free of irq descriptors during cpu up/down In-Reply-To: <55A579FD.6030000@oracle.com> Message-ID: References: <20150705170530.849428850@linutronix.de> <20150705171102.063519515@linutronix.de> <55A51F10.7010407@oracle.com> <55A532C2.4080306@oracle.com> <55A56B48.4060605@oracle.com> <55A579FD.6030000@oracle.com> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1914 Lines: 47 Boris, On Tue, 14 Jul 2015, Boris Ostrovsky wrote: > On 07/14/2015 04:15 PM, Thomas Gleixner wrote: > > > > The issue here is that all architectures need that protection and just > > > > Xen does irq allocations in cpu_up. > > > > > > > > So moving that protection into architecture code is not really an > > > > option. > > > > > > > > > > > Otherwise we will need to have something like arch_post_cpu_up() > > > > > > > after the lock is released. > > > > I'm not sure, that this will work. You probably want to do this in the > > > > cpu prepare stage, i.e. before calling __cpu_up(). > > > For PV guests (the ones that use xen_cpu_up()) it will work either before > > > or > > > after __cpu_up(). At least my (somewhat limited) testing didn't show any > > > problems so far. > > > > > > However, HVM CPUs use xen_hvm_cpu_up() and if you read comments there you > > > will > > > see that xen_smp_intr_init() needs to be called before native_cpu_up() but > > > xen_init_lock_cpu() (which eventually calls irq_alloc_descs()) needs to be > > > called after. > > > > > > I think I can split xen_init_lock_cpu() so that the part that needs to be > > > called after will avoid going into irq core code. And then the rest will > > > go > > > into arch_cpu_prepare(). > > I think we should revisit this for 4.3. For 4.2 we can do the trivial > > variant and move the locking in native_cpu_up() and x86 only. x86 was > > the only arch on which such wreckage has been seen in the wild, but we > > should have that protection for all archs in the long run. > > > > Patch below should fix the issue. > > Thanks! Most of my tests passed, I had a couple of failures but I will need to > see whether they are related to this patch. Did you ever come around to address that irq allocation from within cpu_up()? I really want to generalize the protection instead of carrying that x86 only hack forever. Thanks, tglx