Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752457AbaBMRpq (ORCPT ); Thu, 13 Feb 2014 12:45:46 -0500 Received: from mx1.redhat.com ([209.132.183.28]:17005 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752367AbaBMRpl (ORCPT ); Thu, 13 Feb 2014 12:45:41 -0500 Date: Thu, 13 Feb 2014 18:44:52 +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: <20140213174452.GB14455@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> <20140211171553.GA26036@redhat.com> <52FA7539.4030907@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <52FA7539.4030907@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 02/12, Srivatsa S. Bhat wrote: > > On 02/11/2014 10:45 PM, Oleg Nesterov wrote: > > > > I am a bit confused... If we do this, why we can't simply turn > > cpu_add_remove_lock into rw_semaphore? [...snip...] > cpu_notifier_register_begin(); | Run in parallel > | with similar phases > for_each_online_cpu(cpu) | from other subsystems. > init_cpu(cpu); | > > /* Updates the cpu notifier chain. */ > register_cpu_notifier(&foobar_cpu_notifier); ||| -- Must run serially Ah indeed, we can't use a single lock, thanks. Perhaps we can simply add a spinlock_t which only protects cpu_chain though, but I am not sure and currently this is off-topic anyway. Thanks, 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/