Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752039AbaBNGrS (ORCPT ); Fri, 14 Feb 2014 01:47:18 -0500 Received: from e28smtp02.in.ibm.com ([122.248.162.2]:60343 "EHLO e28smtp02.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751547AbaBNGrR (ORCPT ); Fri, 14 Feb 2014 01:47:17 -0500 Message-ID: <52FDBBE8.2040709@linux.vnet.ibm.com> Date: Fri, 14 Feb 2014 12:17:04 +0530 From: Madhavan Srinivasan User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: "Srivatsa S. Bhat" , 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, Benjamin Herrenschmidt , Olof Johansson , Wang Dongsheng , linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH 13/51] powerpc, sysfs: Fix CPU hotplug callback registration References: <20140205220251.19080.92336.stgit@srivatsabhat.in.ibm.com> <20140205220654.19080.11341.stgit@srivatsabhat.in.ibm.com> In-Reply-To: <20140205220654.19080.11341.stgit@srivatsabhat.in.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14021406-5816-0000-0000-00000C450E9D Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thursday 06 February 2014 03:36 AM, 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 sysfs code in powerpc by using this latter form of callback > registration. Acked-by: Madhavan Srinivasan > > Cc: Benjamin Herrenschmidt > Cc: Paul Mackerras > Cc: Madhavan Srinivasan > Cc: Olof Johansson > Cc: Wang Dongsheng > Cc: linuxppc-dev@lists.ozlabs.org > Signed-off-by: Srivatsa S. Bhat > --- > > arch/powerpc/kernel/sysfs.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c > index 97e1dc9..c29ad44 100644 > --- a/arch/powerpc/kernel/sysfs.c > +++ b/arch/powerpc/kernel/sysfs.c > @@ -975,7 +975,8 @@ static int __init topology_init(void) > int cpu; > > register_nodes(); > - register_cpu_notifier(&sysfs_cpu_nb); > + > + cpu_maps_update_begin(); > > for_each_possible_cpu(cpu) { > struct cpu *c = &per_cpu(cpu_devices, cpu); > @@ -999,6 +1000,11 @@ static int __init topology_init(void) > if (cpu_online(cpu)) > register_cpu_online(cpu); > } > + > + __register_cpu_notifier(&sysfs_cpu_nb); > + > + cpu_maps_update_done(); > + > #ifdef CONFIG_PPC64 > sysfs_create_dscr_default(); > #endif /* CONFIG_PPC64 */ > -- 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/