From mboxrd@z Thu Jan 1 00:00:00 1970 From: Guenter Roeck Date: Thu, 06 Feb 2014 01:25:31 +0000 Subject: Re: [lm-sensors] [PATCH 42/51] hwmon, coretemp: Fix CPU hotplug callback registration Message-Id: <20140206012531.GA3887@roeck-us.net> List-Id: References: <20140205220251.19080.92336.stgit@srivatsabhat.in.ibm.com> <20140205221205.19080.15108.stgit@srivatsabhat.in.ibm.com> <20140206004412.GA1308@roeck-us.net> In-Reply-To: <20140206004412.GA1308@roeck-us.net> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: "Srivatsa S. Bhat" Cc: paulus@samba.org, oleg@redhat.com, rusty@rustcorp.com.au, peterz@infradead.org, tglx@linutronix.de, akpm@linux-foundation.org, 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, Fenghua Yu , Jean Delvare , lm-sensors@lm-sensors.org On Wed, Feb 05, 2014 at 04:44:12PM -0800, Guenter Roeck wrote: > On Thu, Feb 06, 2014 at 03:42:06AM +0530, Srivatsa S. Bhat wrote: > > 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 hwmon coretemp code by using this latter form of callback > > registration. > > > > Cc: Fenghua Yu > > Cc: Jean Delvare > > Cc: Guenter Roeck > > Cc: lm-sensors@lm-sensors.org > > Signed-off-by: Srivatsa S. Bhat > > Applied. > That obviously doesn't build ;-). Replace with Acked-by: Guenter Roeck Guenter _______________________________________________ lm-sensors mailing list lm-sensors@lm-sensors.org http://lists.lm-sensors.org/mailman/listinfo/lm-sensors From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753996AbaBFBZf (ORCPT ); Wed, 5 Feb 2014 20:25:35 -0500 Received: from mail-pb0-f68.google.com ([209.85.160.68]:57770 "EHLO mail-pb0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751769AbaBFBZd (ORCPT ); Wed, 5 Feb 2014 20:25:33 -0500 Date: Wed, 5 Feb 2014 17:25:31 -0800 From: Guenter Roeck To: "Srivatsa S. Bhat" Cc: paulus@samba.org, oleg@redhat.com, rusty@rustcorp.com.au, peterz@infradead.org, tglx@linutronix.de, akpm@linux-foundation.org, 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, Fenghua Yu , Jean Delvare , lm-sensors@lm-sensors.org Subject: Re: [PATCH 42/51] hwmon, coretemp: Fix CPU hotplug callback registration Message-ID: <20140206012531.GA3887@roeck-us.net> References: <20140205220251.19080.92336.stgit@srivatsabhat.in.ibm.com> <20140205221205.19080.15108.stgit@srivatsabhat.in.ibm.com> <20140206004412.GA1308@roeck-us.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140206004412.GA1308@roeck-us.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 05, 2014 at 04:44:12PM -0800, Guenter Roeck wrote: > On Thu, Feb 06, 2014 at 03:42:06AM +0530, Srivatsa S. Bhat wrote: > > 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 hwmon coretemp code by using this latter form of callback > > registration. > > > > Cc: Fenghua Yu > > Cc: Jean Delvare > > Cc: Guenter Roeck > > Cc: lm-sensors@lm-sensors.org > > Signed-off-by: Srivatsa S. Bhat > > Applied. > That obviously doesn't build ;-). Replace with Acked-by: Guenter Roeck Guenter