From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0896EC3A5A7 for ; Wed, 4 Sep 2019 13:17:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D542C2168B for ; Wed, 4 Sep 2019 13:17:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730533AbfIDNRn (ORCPT ); Wed, 4 Sep 2019 09:17:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38596 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730269AbfIDNRl (ORCPT ); Wed, 4 Sep 2019 09:17:41 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 7553A18C4283; Wed, 4 Sep 2019 13:17:40 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.63]) by smtp.corp.redhat.com (Postfix) with SMTP id 549DB194B2; Wed, 4 Sep 2019 13:17:37 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 4 Sep 2019 15:17:38 +0200 (CEST) Date: Wed, 4 Sep 2019 15:17:35 +0200 From: Oleg Nesterov To: Peter Zijlstra Cc: Mathieu Desnoyers , paulmck , Linus Torvalds , linux-kernel , "Eric W. Biederman" , "Russell King, ARM Linux" , Chris Metcalf , Chris Lameter , Kirill Tkhai , Mike Galbraith , Thomas Gleixner , Ingo Molnar Subject: Re: [RFC PATCH 1/2] Fix: sched/membarrier: p->mm->membarrier_state racy load Message-ID: <20190904131734.GD24568@redhat.com> References: <20190903201135.1494-1-mathieu.desnoyers@efficios.com> <20190903202434.GX2349@hirez.programming.kicks-ass.net> <1029906102.725.1567543307658.JavaMail.zimbra@efficios.com> <20190904112819.GD2349@hirez.programming.kicks-ass.net> <20190904120336.GC24568@redhat.com> <20190904124333.GQ2332@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190904124333.GQ2332@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.62]); Wed, 04 Sep 2019 13:17:40 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/04, Peter Zijlstra wrote: > > On Wed, Sep 04, 2019 at 02:03:37PM +0200, Oleg Nesterov wrote: > > On 09/04, Peter Zijlstra wrote: > > > > > > + struct task_struct *g, *t; > > > + > > > + read_lock(&tasklist_lock); > > > + do_each_thread(g, t) { > > > > for_each_process_thread() looks better > > Argh, I always get confused. Why do we have multiple version of this > again? Because I am lazy ;) but actually for_each_process_thread() is suboptimal, I think you need for_each_process(p) { if (p->flags & PF_KTHREAD) continue; if (p->mm != mm) continue; for_each_thread(p, t) atomic_or(t->membarrier_state, ...); } to avoid unnecessary each-thread when group leader has another ->mm. Unfortunately a zombie leader has ->mm == NULL, so perhaps something like for_each_process(p) { if (p->flags & PF_KTHREAD) continue; for_each_thread(p, t) { if (unlikely(!t->mm)) continue; if (t->mm != mm) break; atomic_or(t->membarrier_state, ...); } } and to we really need the new atomic_t member? can we use t->atomic_flags and add PFA_MEMBARRIER_EXPEDITED ? Oleg.