Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755744AbaBEWPg (ORCPT ); Wed, 5 Feb 2014 17:15:36 -0500 Received: from e28smtp05.in.ibm.com ([122.248.162.5]:36772 "EHLO e28smtp05.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755692AbaBEWP3 (ORCPT ); Wed, 5 Feb 2014 17:15:29 -0500 From: "Srivatsa S. Bhat" Subject: [PATCH 30/51] powercap, intel-rapl: 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, "Rafael J. Wysocki" , Jacob Pan , Srinivas Pandruvada , "Srivatsa S. Bhat" Date: Thu, 06 Feb 2014 03:40:07 +0530 Message-ID: <20140205221006.19080.85166.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: 14020522-8256-0000-0000-00000B524C49 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 intel-rapl code in the powercap driver by using this latter form of callback registration. But retain the calls to get/put_online_cpus(), since they also protect the function rapl_cleanup_data(). By nesting get/put_online_cpus() *inside* cpu_maps_update_begin/done(), we avoid the ABBA deadlock possibility mentioned above. Cc: "Rafael J. Wysocki" Cc: Jacob Pan Cc: Srinivas Pandruvada Signed-off-by: Srivatsa S. Bhat --- drivers/powercap/intel_rapl.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/drivers/powercap/intel_rapl.c b/drivers/powercap/intel_rapl.c index 3c67683..b460d46 100644 --- a/drivers/powercap/intel_rapl.c +++ b/drivers/powercap/intel_rapl.c @@ -1369,6 +1369,9 @@ static int __init rapl_init(void) return -ENODEV; } + + cpu_maps_update_begin(); + /* prevent CPU hotplug during detection */ get_online_cpus(); ret = rapl_detect_topology(); @@ -1380,20 +1383,23 @@ static int __init rapl_init(void) ret = -ENODEV; goto done; } - register_hotcpu_notifier(&rapl_cpu_notifier); + __register_hotcpu_notifier(&rapl_cpu_notifier); done: put_online_cpus(); + cpu_maps_update_done(); return ret; } static void __exit rapl_exit(void) { + cpu_maps_update_begin(); get_online_cpus(); - unregister_hotcpu_notifier(&rapl_cpu_notifier); + __unregister_hotcpu_notifier(&rapl_cpu_notifier); rapl_unregister_powercap(); rapl_cleanup_data(); put_online_cpus(); + cpu_maps_update_done(); } module_init(rapl_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/