Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752587AbaBKRRZ (ORCPT ); Tue, 11 Feb 2014 12:17:25 -0500 Received: from mx1.redhat.com ([209.132.183.28]:16345 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752432AbaBKRRW (ORCPT ); Tue, 11 Feb 2014 12:17:22 -0500 Date: Tue, 11 Feb 2014 18:15:53 +0100 From: Oleg Nesterov To: "Srivatsa S. Bhat" Cc: Toshi Kani , paulus@samba.org, 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, "Rafael J. Wysocki" Subject: Re: [PATCH 01/51] CPU hotplug: Provide lockless versions of callback registration functions Message-ID: <20140211171553.GA26036@redhat.com> References: <20140205220251.19080.92336.stgit@srivatsabhat.in.ibm.com> <20140205220447.19080.9460.stgit@srivatsabhat.in.ibm.com> <1392081980.5612.123.camel@misato.fc.hp.com> <52F9ED11.5010800@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <52F9ED11.5010800@linux.vnet.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/11, Srivatsa S. Bhat wrote: > > +static DECLARE_RWSEM(cpu_hotplug_rwsem); > + > +void cpu_notifier_register_begin(void) > +{ > + down_read(&cpu_hotplug_rwsem); > +} > + > +void cpu_notifier_register_end(void) > +{ > + up_read(&cpu_hotplug_rwsem); > +} > + > /* Serializes the updates to cpu_online_mask, cpu_present_mask */ > static DEFINE_MUTEX(cpu_add_remove_lock); > > @@ -32,12 +45,14 @@ static DEFINE_MUTEX(cpu_add_remove_lock); > */ > void cpu_maps_update_begin(void) > { > + down_write(&cpu_hotplug_rwsem); > mutex_lock(&cpu_add_remove_lock); > } > > void cpu_maps_update_done(void) > { > mutex_unlock(&cpu_add_remove_lock); > + up_write(&cpu_hotplug_rwsem); > } I am a bit confused... If we do this, why we can't simply turn cpu_add_remove_lock into rw_semaphore? Oleg. -- 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/