Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755521AbaBEWPB (ORCPT ); Wed, 5 Feb 2014 17:15:01 -0500 Received: from e28smtp08.in.ibm.com ([122.248.162.8]:57418 "EHLO e28smtp08.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752800AbaBEWO4 (ORCPT ); Wed, 5 Feb 2014 17:14:56 -0500 From: "Srivatsa S. Bhat" Subject: [PATCH 27/51] x86, kvm: Fix CPU hotplug callback registration To: paulus@samba.org, oleg@redhat.com, rusty@rustcorp.com.au, peterz@infradead.org, tglx@linutronix.de, akpm@linux-foundation.org Cc: mingo@kernel.org, paulmck@linux.vnet.ibm.com, tj@kernel.org, walken@google.com, ego@linux.vnet.ibm.com, linux@arm.linux.org.uk, linux-kernel@vger.kernel.org, srivatsa.bhat@linux.vnet.ibm.com, Gleb Natapov , Paolo Bonzini , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, kvm@vger.kernel.org, "Srivatsa S. Bhat" Date: Thu, 06 Feb 2014 03:39:35 +0530 Message-ID: <20140205220934.19080.30046.stgit@srivatsabhat.in.ibm.com> In-Reply-To: <20140205220251.19080.92336.stgit@srivatsabhat.in.ibm.com> References: <20140205220251.19080.92336.stgit@srivatsabhat.in.ibm.com> User-Agent: StGIT/0.14.3 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14020522-2000-0000-0000-00000F986A31 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Subsystems that want to register CPU hotplug callbacks, as well as perform initialization for the CPUs that are already online, often do it as shown below: get_online_cpus(); for_each_online_cpu(cpu) init_cpu(cpu); register_cpu_notifier(&foobar_cpu_notifier); put_online_cpus(); This is wrong, since it is prone to ABBA deadlocks involving the cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently with CPU hotplug operations). Instead, the correct and race-free way of performing the callback registration is: cpu_maps_update_begin(); for_each_online_cpu(cpu) init_cpu(cpu); /* Note the use of the double underscored version of the API */ __register_cpu_notifier(&foobar_cpu_notifier); cpu_maps_update_done(); Fix the kvm code in x86 by using this latter form of callback registration. Cc: Gleb Natapov Cc: Paolo Bonzini Cc: Thomas Gleixner Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: x86@kernel.org Cc: kvm@vger.kernel.org Signed-off-by: Srivatsa S. Bhat --- arch/x86/kvm/x86.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 39c28f09..e3893b7 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -5365,7 +5365,8 @@ static void kvm_timer_init(void) int cpu; max_tsc_khz = tsc_khz; - register_hotcpu_notifier(&kvmclock_cpu_notifier_block); + + cpu_maps_update_begin(); if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) { #ifdef CONFIG_CPU_FREQ struct cpufreq_policy policy; @@ -5382,6 +5383,10 @@ static void kvm_timer_init(void) pr_debug("kvm: max_tsc_khz = %ld\n", max_tsc_khz); for_each_online_cpu(cpu) smp_call_function_single(cpu, tsc_khz_changed, NULL, 1); + + __register_hotcpu_notifier(&kvmclock_cpu_notifier_block); + cpu_maps_update_done(); + } static DEFINE_PER_CPU(struct kvm_vcpu *, current_vcpu); -- 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/