Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754917AbaBEWMm (ORCPT ); Wed, 5 Feb 2014 17:12:42 -0500 Received: from e28smtp08.in.ibm.com ([122.248.162.8]:39711 "EHLO e28smtp08.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752553AbaBEWMk (ORCPT ); Wed, 5 Feb 2014 17:12:40 -0500 From: "Srivatsa S. Bhat" Subject: [PATCH 15/51] x86, cpuid: 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, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , x86@kernel.org, "Srivatsa S. Bhat" Date: Thu, 06 Feb 2014 03:37:18 +0530 Message-ID: <20140205220717.19080.16368.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: 14020522-2000-0000-0000-00000F9868F2 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 cpuid code in x86 by using this latter form of callback registration. Cc: "H. Peter Anvin" Cc: Thomas Gleixner Cc: Ingo Molnar Cc: x86@kernel.org Signed-off-by: Srivatsa S. Bhat --- arch/x86/kernel/cpuid.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) diff --git a/arch/x86/kernel/cpuid.c b/arch/x86/kernel/cpuid.c index 7d9481c..1df179a 100644 --- a/arch/x86/kernel/cpuid.c +++ b/arch/x86/kernel/cpuid.c @@ -198,14 +198,15 @@ static int __init cpuid_init(void) goto out_chrdev; } cpuid_class->devnode = cpuid_devnode; - get_online_cpus(); + + cpu_maps_update_begin(); for_each_online_cpu(i) { err = cpuid_device_create(i); if (err != 0) goto out_class; } - register_hotcpu_notifier(&cpuid_class_cpu_notifier); - put_online_cpus(); + __register_hotcpu_notifier(&cpuid_class_cpu_notifier); + cpu_maps_update_done(); err = 0; goto out; @@ -215,7 +216,7 @@ out_class: for_each_online_cpu(i) { cpuid_device_destroy(i); } - put_online_cpus(); + cpu_maps_update_done(); class_destroy(cpuid_class); out_chrdev: __unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid"); @@ -227,13 +228,13 @@ static void __exit cpuid_exit(void) { int cpu = 0; - get_online_cpus(); + cpu_maps_update_begin(); for_each_online_cpu(cpu) cpuid_device_destroy(cpu); class_destroy(cpuid_class); __unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid"); - unregister_hotcpu_notifier(&cpuid_class_cpu_notifier); - put_online_cpus(); + __unregister_hotcpu_notifier(&cpuid_class_cpu_notifier); + cpu_maps_update_done(); } module_init(cpuid_init); -- 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/