From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755729Ab1FPTA3 (ORCPT ); Thu, 16 Jun 2011 15:00:29 -0400 Received: from casper.infradead.org ([85.118.1.10]:36254 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754559Ab1FPTA0 convert rfc822-to-8bit (ORCPT ); Thu, 16 Jun 2011 15:00:26 -0400 Subject: Re: [PATCH 1/3] stop_machine: kill __stop_machine() From: Peter Zijlstra To: Suresh Siddha Cc: Tejun Heo , "x86@kernel.org" , "mingo@elte.hu" , "akpm@linux-foundation.org" , "torvalds@linux-foundation.org" , "linux-kernel@vger.kernel.org" In-Reply-To: <1308245872.2682.369.camel@sbsiddha-MOBL3.sc.intel.com> References: <1308071218-5912-1-git-send-email-tj@kernel.org> <1308071218-5912-2-git-send-email-tj@kernel.org> <1308226372.13240.42.camel@twins> <1308245872.2682.369.camel@sbsiddha-MOBL3.sc.intel.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Thu, 16 Jun 2011 19:55:10 +0200 Message-ID: <1308246910.13240.238.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2011-06-16 at 10:37 -0700, Suresh Siddha wrote: > On Thu, 2011-06-16 at 05:12 -0700, Peter Zijlstra wrote: > > On Tue, 2011-06-14 at 19:06 +0200, Tejun Heo wrote: > > Please have a look at: > > > > --- > > commit d91309f69b7bdb64aeb30106fde8d18c5dd354b5 > > Author: Peter Zijlstra > > Date: Fri Feb 11 22:07:46 2011 +0100 > > > > x86: Fix text_poke_smp_batch() deadlock > > > > Fix this deadlock - we are already holding the mutex: > > > ... > > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > > index 1236085..7038b95 100644 > > --- a/arch/x86/kernel/alternative.c > > +++ b/arch/x86/kernel/alternative.c > > @@ -671,7 +671,7 @@ void __kprobes text_poke_smp_batch(struct text_poke_param *params, int n) > > > > atomic_set(&stop_machine_first, 1); > > wrote_text = 0; > > - stop_machine(stop_machine_text_poke, (void *)&tpp, NULL); > > + __stop_machine(stop_machine_text_poke, (void *)&tpp, NULL); > > } > > > > #if defined(CONFIG_DYNAMIC_FTRACE) || defined(HAVE_JUMP_LABEL) > > > > Peter, So it looks like we are allowing a new cpu to come online in > parallel, while we poke the text? Isn't it a problem? What am I missing? the caller already did get_online_cpus(), do_optimize_kprobes() get_online_cpus() arch_optimize_kprobes() text_poke_smp_batch() put_online_cpus()