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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 7E458C49ED7 for ; Fri, 13 Sep 2019 15:21:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5349F20640 for ; Fri, 13 Sep 2019 15:21:05 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="J9wIDRik" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2403886AbfIMPVE (ORCPT ); Fri, 13 Sep 2019 11:21:04 -0400 Received: from mail.efficios.com ([167.114.142.138]:56164 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388354AbfIMPVD (ORCPT ); Fri, 13 Sep 2019 11:21:03 -0400 Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id 233132D13B1; Fri, 13 Sep 2019 11:21:02 -0400 (EDT) Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10032) with ESMTP id CFoNyovJVe_P; Fri, 13 Sep 2019 11:20:57 -0400 (EDT) Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id 3EEBF2D13AB; Fri, 13 Sep 2019 11:20:57 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 3EEBF2D13AB DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1568388057; bh=uyjeHRABbg33hV2BOaw8TWyHoPbqXM+813BJEngMtQw=; h=Date:From:To:Message-ID:MIME-Version; b=J9wIDRikZY7PrhNElCf5wOIuUg9NgaBfuo0Xnk1hxPG5kCr/WLon7xAceBqgqbVR+ R9E6wpEISVY0EEruJ6edkV7y0HE446R41OhHKnOd7Ks8BtjYhNTDQZbzg9XWKxLX7a M0T1jBM1QyehUYnTKp0TKz+6MegBsiP5a0ds+oIEVhgVLunV+14Opo65Rkk7snMWBI fr0Jzi6TM1WOUPjUuyGLuXlTCu0+YnKEMX23rfG5cZ2obL2ftkcuddn/0jfGZsDRFT MxmoNKlRw+AlM0A4Mc6dybQVR4ZIuH/6e61xIOX6jpzzAJ1Jc3P3YN3xQSn3DGOUcy yX4vgP1KgYG1w== X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10026) with ESMTP id utNUGfVAnKKJ; Fri, 13 Sep 2019 11:20:57 -0400 (EDT) Received: from mail02.efficios.com (mail02.efficios.com [167.114.142.138]) by mail.efficios.com (Postfix) with ESMTP id 256932D13A2; Fri, 13 Sep 2019 11:20:57 -0400 (EDT) Date: Fri, 13 Sep 2019 11:20:56 -0400 (EDT) From: Mathieu Desnoyers To: Oleg Nesterov Cc: Peter Zijlstra , paulmck , Ingo Molnar , linux-kernel , "Eric W. Biederman" , Linus Torvalds , "Russell King, ARM Linux" , Chris Metcalf , Chris Lameter , Kirill Tkhai , Mike Galbraith , Thomas Gleixner Message-ID: <1629045844.2645.1568388056947.JavaMail.zimbra@efficios.com> In-Reply-To: <20190909110036.GC6719@redhat.com> References: <20190906082305.GU2349@hirez.programming.kicks-ass.net> <20190908134909.12389-1-mathieu.desnoyers@efficios.com> <20190909110036.GC6719@redhat.com> Subject: Re: [RFC PATCH 4/4] Fix: sched/membarrier: p->mm->membarrier_state racy load (v2) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.142.138] X-Mailer: Zimbra 8.8.15_GA_3847 (ZimbraWebClient - FF69 (Linux)/8.8.15_GA_3847) Thread-Topic: sched/membarrier: p->mm->membarrier_state racy load (v2) Thread-Index: SLK12JUbrQMEyYCzu/XRb/7xOGRepw== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On Sep 9, 2019, at 7:00 AM, Oleg Nesterov oleg@redhat.com wrote: > On 09/08, Mathieu Desnoyers wrote: >> >> +static void sync_runqueues_membarrier_state(struct mm_struct *mm) >> +{ >> + int membarrier_state = atomic_read(&mm->membarrier_state); >> + bool fallback = false; >> + cpumask_var_t tmpmask; >> + int cpu; >> + >> + if (atomic_read(&mm->mm_users) == 1 || num_online_cpus() == 1) { >> + WRITE_ONCE(this_rq()->membarrier_state, membarrier_state); > > This doesn't look safe, this caller can migrate to another CPU after > it calculates the per-cpu ptr. > > I think you need do disable preemption or simply use this_cpu_write(). Good point! I'll use this_cpu_write() there and within membarrier_exec_mmap(), which seems to be affected by the same problem. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com