From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753719AbaBOThL (ORCPT ); Sat, 15 Feb 2014 14:37:11 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:53095 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753519AbaBOThI (ORCPT ); Sat, 15 Feb 2014 14:37:08 -0500 Date: Sat, 15 Feb 2014 11:38:28 -0800 From: Greg Kroah-Hartman To: "Srivatsa S. Bhat" Cc: paulus@samba.org, oleg@redhat.com, mingo@kernel.org, rusty@rustcorp.com.au, peterz@infradead.org, tglx@linutronix.de, akpm@linux-foundation.org, 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 Subject: Re: [PATCH v2 38/52] drivers/base/topology.c: Fix CPU hotplug callback registration Message-ID: <20140215193828.GA25619@kroah.com> References: <20140214074750.22701.47330.stgit@srivatsabhat.in.ibm.com> <20140214075750.22701.57260.stgit@srivatsabhat.in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140214075750.22701.57260.stgit@srivatsabhat.in.ibm.com> User-Agent: Mutt/1.5.22 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 14, 2014 at 01:27:51PM +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_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 topology code by using this latter form of callback registration. > > Cc: Greg Kroah-Hartman > Cc: Ingo Molnar > Signed-off-by: Srivatsa S. Bhat Acked-by: Greg Kroah-Hartman