Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753222AbaBEXln (ORCPT ); Wed, 5 Feb 2014 18:41:43 -0500 Received: from cdptpa-outbound-snat.email.rr.com ([107.14.166.226]:3155 "EHLO cdptpa-oedge-vip.email.rr.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751387AbaBEXll (ORCPT ); Wed, 5 Feb 2014 18:41:41 -0500 Date: Wed, 5 Feb 2014 18:41:38 -0500 From: Steven Rostedt 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, Frederic Weisbecker , Ingo Molnar Subject: Re: [PATCH 46/51] trace, ring-buffer: Fix CPU hotplug callback registration Message-ID: <20140205184138.10f8cd15@gandalf.local.home> In-Reply-To: <20140205221257.19080.88037.stgit@srivatsabhat.in.ibm.com> References: <20140205220251.19080.92336.stgit@srivatsabhat.in.ibm.com> <20140205221257.19080.88037.stgit@srivatsabhat.in.ibm.com> X-Mailer: Claws Mail 3.9.3 (GTK+ 2.24.22; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-RR-Connecting-IP: 107.14.168.130:25 X-Cloudmark-Score: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 06 Feb 2014 03:42:58 +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 tracing ring-buffer code by using this latter form of callback > registration. > > Cc: Steven Rostedt > Cc: Frederic Weisbecker > Cc: Ingo Molnar > Signed-off-by: Srivatsa S. Bhat > Acked-by: Steven Rostedt -- Steve -- 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/