From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e23smtp09.au.ibm.com ([202.81.31.142]:43162 "EHLO e23smtp09.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753086AbaBNICC (ORCPT ); Fri, 14 Feb 2014 03:02:02 -0500 Received: from /spool/local by e23smtp09.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 14 Feb 2014 18:02:00 +1000 From: "Srivatsa S. Bhat" Subject: [PATCH v2 32/52] powercap, intel-rapl: Fix CPU hotplug callback registration Date: Fri, 14 Feb 2014 13:26:27 +0530 Message-ID: <20140214075626.22701.37887.stgit@srivatsabhat.in.ibm.com> In-Reply-To: <20140214074750.22701.47330.stgit@srivatsabhat.in.ibm.com> References: <20140214074750.22701.47330.stgit@srivatsabhat.in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: paulus@samba.org, oleg@redhat.com, mingo@kernel.org, rusty@rustcorp.com.au, peterz@infradead.org, tglx@linutronix.de, akpm@linux-foundation.org Cc: paulmck@linux.vnet.ibm.com, tj@kernel.org, walken@google.com, ego@linux.vnet.ibm.com, linux@arm.linux.org.uk, rjw@rjwysocki.net, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, srivatsa.bhat@linux.vnet.ibm.com"Rafael J. Wysocki" , Jacob Pan , Srinivas Pandruvada "Srivatsa S. Bhat" Message-ID: <20140214075627.5NLqZidWOPiS2zGTiXiOKtCg3NR-dqeVGk1Jbs_ov1A@z> 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_notifier_register_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_notifier_register_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_notifier_register_begin/done(), we avoid the ABBA deadlock possibility mentioned above. Cc: "Rafael J. Wysocki" Cc: Jacob Pan Cc: Srinivas Pandruvada Cc: Ingo Molnar 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..d6c74c1 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_notifier_register_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_notifier_register_done(); return ret; } static void __exit rapl_exit(void) { + cpu_notifier_register_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_notifier_register_done(); } module_init(rapl_init);