From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753885Ab1FTKVq (ORCPT ); Mon, 20 Jun 2011 06:21:46 -0400 Received: from merlin.infradead.org ([205.233.59.134]:36808 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753206Ab1FTKVo convert rfc822-to-8bit (ORCPT ); Mon, 20 Jun 2011 06:21:44 -0400 Subject: Re: [tip:sched/urgent] cpuset: Fix cpuset_cpus_allowed_fallback(), don't update tsk->rt.nr_cpus_allowed From: Peter Zijlstra To: mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, tglx@linutronix.de, oleg@redhat.com, kosaki.motohiro@jp.fujitsu.com, mingo@elte.hu Cc: linux-tip-commits@vger.kernel.org In-Reply-To: References: <4DD4B3FA.5060901@jp.fujitsu.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Mon, 20 Jun 2011 12:20:58 +0200 Message-ID: <1308565258.26237.2.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 Sat, 2011-05-28 at 16:35 +0000, tip-bot for KOSAKI Motohiro wrote: > +++ b/kernel/kthread.c > @@ -202,8 +202,8 @@ void kthread_bind(struct task_struct *p, unsigned int cpu) > return; > } > > - p->cpus_allowed = cpumask_of_cpu(cpu); > - p->rt.nr_cpus_allowed = 1; > + /* It's safe because the task is inactive. */ > + do_set_cpus_allowed(p, cpumask_of(cpu)); > p->flags |= PF_THREAD_BOUND; > } I just happened to be staring at this stuff again, and I'm wondering how and why this is correct. After kthread_create() the thread exists and is exposed in the pid-hash, therefore userspace can come and do sys_sched_setaffinity() on it, and since we're not holding any locks and set PF_THREAD_BOUND _after_ setting cpus_allowed, things can end up funny. Hmm?