Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752753AbYKKQIW (ORCPT ); Tue, 11 Nov 2008 11:08:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751459AbYKKQIL (ORCPT ); Tue, 11 Nov 2008 11:08:11 -0500 Received: from mx2.redhat.com ([66.187.237.31]:41774 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751458AbYKKQIK (ORCPT ); Tue, 11 Nov 2008 11:08:10 -0500 Date: Tue, 11 Nov 2008 18:03:27 +0100 From: Oleg Nesterov To: "Paul E. McKenney" Cc: Heiko Carstens , Ingo Molnar , "Rafael J. Wysocki" , Linux Kernel Mailing List , Kernel Testers List , Rusty Russell , Vegard Nossum , Peter Zijlstra , Dmitry Adamushko , Andrew Morton , Steven Rostedt Subject: Q: force_quiescent_state && cpu_online_map Message-ID: <20081111170327.GB18214@redhat.com> References: <20081110120401.GA15518@osiris.boeblingen.de.ibm.com> <200811101547.21325.rjw@sisk.pl> <200811102355.42389.rjw@sisk.pl> <20081111105214.GA15645@elte.hu> <20081111113134.GA5653@osiris.boeblingen.de.ibm.com> <20081111124201.GA9459@osiris.boeblingen.de.ibm.com> <20081111143505.GA6923@linux.vnet.ibm.com> <20081111150225.GA10743@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081111150225.GA10743@linux.vnet.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1640 Lines: 51 I don't think this matters, but still... force_quiescent_state: * cpu_online_map is updated by the _cpu_down() * using __stop_machine(). Since we're in irqs disabled * section, __stop_machine() is not exectuting, hence * the cpu_online_map is stable. * * However, a cpu might have been offlined _just_ before * we disabled irqs while entering here. * And rcu subsystem might not yet have handled the CPU_DEAD * notification, leading to the offlined cpu's bit * being set in the rcp->cpumask. * * Hence cpumask = (rcp->cpumask & cpu_online_map) to prevent * sending smp_reschedule() to an offlined CPU. */ cpus_and(cpumask, rcp->cpumask, cpu_online_map); cpu_clear(rdp->cpu, cpumask); for_each_cpu_mask_nr(cpu, cpumask) smp_send_reschedule(cpu); However, // called by __stop_machine take_cpu_down() arch/x86/kernel/smpboot.c:cpu_disable_common() /* * HACK: * Allow any queued timer interrupts to get serviced * This is only a temporary solution until we cleanup * fixup_irqs as we do for IA64. */ local_irq_enable(); mdelay(1); local_irq_disable(); ... remove_cpu_from_maps(cpu); So it is possible to send the ipi to the dying CPU. I know nothing about this low-level irq code, most probably this is harmless. We already did clear_local_APIC(), but I don't understand what it does. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/