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=-2.5 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 5D271C0650E for ; Mon, 1 Jul 2019 09:24:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2A2252089C for ; Mon, 1 Jul 2019 09:24:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728372AbfGAJYi (ORCPT ); Mon, 1 Jul 2019 05:24:38 -0400 Received: from foss.arm.com ([217.140.110.172]:58480 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728143AbfGAJYi (ORCPT ); Mon, 1 Jul 2019 05:24:38 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E933DCFC; Mon, 1 Jul 2019 02:24:37 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 94F433F718; Mon, 1 Jul 2019 02:24:36 -0700 (PDT) Date: Mon, 1 Jul 2019 10:24:30 +0100 From: Mark Rutland To: Peter Zijlstra Cc: Alexander Shishkin , Arnaldo Carvalho de Melo , Ingo Molnar , linux-kernel@vger.kernel.org, jolsa@redhat.com, dvyukov@google.com, namhyung@kernel.org, xiexiuqi@huawei.com, syzbot+a24c397a29ad22d86c98@syzkaller.appspotmail.com Subject: Re: [PATCH] perf: Fix race between close() and fork() Message-ID: <20190701092429.GA10975@lakrids.cambridge.arm.com> References: <278ac311-d8f3-2832-5fa1-522471c8c31c@huawei.com> <20190228140109.64238-1-alexander.shishkin@linux.intel.com> <20190308155429.GB10860@lakrids.cambridge.arm.com> <20190624121902.GE3436@hirez.programming.kicks-ass.net> <20190625084904.GY3463@hirez.programming.kicks-ass.net> <20190625104320.GZ3463@hirez.programming.kicks-ass.net> <20190628165003.GA5143@lakrids.cambridge.arm.com> <20190628204608.GG3402@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190628204608.GG3402@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 28, 2019 at 10:46:08PM +0200, Peter Zijlstra wrote: > On Fri, Jun 28, 2019 at 05:50:03PM +0100, Mark Rutland wrote: > > > + /* > > > + * Wake any perf_event_free_task() waiting for this event to be > > > + * freed. > > > + */ > > > + smp_mb(); /* pairs with wait_var_event() */ > > > + wake_up_var(var); > > > > Huh, so wake_up_var() doesn't imply a RELEASE? > > > > As an aside, doesn't that mean all callers of wake_up_var() have to do > > likewise to ensure it isn't re-ordered with whatever prior stuff they're > > trying to notify waiters about? Several do an smp_store_release() then a > > wake_up_var(), but IIUC the wake_up_var() could get pulled before that > > release... > > Yah,... > > https://lkml.kernel.org/r/20190624165012.GH3436@hirez.programming.kicks-ass.net That gets me a 404, so I'll assume that's a speculative store. ;) > I needs to get back to that. Ouch; sorry for reminding you of this mess! Thanks, Mark.