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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 94AA1C433EF for ; Wed, 12 Jan 2022 16:13:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343653AbiALQNn (ORCPT ); Wed, 12 Jan 2022 11:13:43 -0500 Received: from mail.efficios.com ([167.114.26.124]:60272 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240511AbiALQNm (ORCPT ); Wed, 12 Jan 2022 11:13:42 -0500 Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id 3D76625724E; Wed, 12 Jan 2022 11:13:42 -0500 (EST) Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id oua0xcW-gUeM; Wed, 12 Jan 2022 11:13:42 -0500 (EST) Received: from localhost (localhost [127.0.0.1]) by mail.efficios.com (Postfix) with ESMTP id E84FB2574CA; Wed, 12 Jan 2022 11:13:41 -0500 (EST) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com E84FB2574CA DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1642004021; bh=4vn/hFKG6knqUORtHXUNl85gRLBGKGI5ehyXZmeHqiE=; h=Date:From:To:Message-ID:MIME-Version; b=nypU3HUYqIBGW8Ug/4thPwW+6ZNBoxBGJ5vAS/oGyRU3w1zsewn5/0zNCS2ErMBsC 5eOjQvarxqF7Tehg3LrybrjVz543f9r1MFzcBgs9fyG2Qx4s1Kk1rl1PUd0lsP3rAn LigLGhFWyNUql6qbltmbg5lm+7WF8G1dzoFxkSn7iuOulhDqth4K5BGNgXLRONIft7 gCeW65+QlWeKXgxh+5dNka6VZJGE+7Mq4K6eW2I7K3ZRCAe5PKR9WJTXIvJZ/vT4ab CLThBc1hHIt6jJlIWT88pvxr1RqWhVdJmecFqBn7QxlPtZsD877wf5lREBjtTRw+4f agzuFVgRDbtDA== X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([127.0.0.1]) by localhost (mail03.efficios.com [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id 9B90cHwpQFb2; Wed, 12 Jan 2022 11:13:41 -0500 (EST) Received: from mail03.efficios.com (mail03.efficios.com [167.114.26.124]) by mail.efficios.com (Postfix) with ESMTP id D721A2572E7; Wed, 12 Jan 2022 11:13:41 -0500 (EST) Date: Wed, 12 Jan 2022 11:13:41 -0500 (EST) From: Mathieu Desnoyers To: Andy Lutomirski Cc: Andrew Morton , linux-mm , Nicholas Piggin , Anton Blanchard , Benjamin Herrenschmidt , Paul Mackerras , Randy Dunlap , linux-arch , x86 , riel , Dave Hansen , Peter Zijlstra , Nadav Amit Message-ID: <1680283915.24784.1642004021846.JavaMail.zimbra@efficios.com> In-Reply-To: References: Subject: Re: [PATCH 08/23] membarrier: Remove redundant clear of mm->membarrier_state in exec_mmap() MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.26.124] X-Mailer: Zimbra 8.8.15_GA_4180 (ZimbraWebClient - FF96 (Linux)/8.8.15_GA_4177) Thread-Topic: membarrier: Remove redundant clear of mm->membarrier_state in exec_mmap() Thread-Index: yWF6Tz08UZu1y1sGy8W9Q/hxbmkICg== Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org ----- On Jan 8, 2022, at 11:43 AM, Andy Lutomirski luto@kernel.org wrote: > exec_mmap() supplies a brand-new mm from mm_alloc(), and membarrier_state > is already 0. There's no need to clear it again. Then I suspect we might want to tweak the comment just above the memory barrier ? /* * Issue a memory barrier before clearing membarrier_state to * guarantee that no memory access prior to exec is reordered after * clearing this state. */ Is that barrier still needed ? Thanks, Mathieu > > Signed-off-by: Andy Lutomirski > --- > kernel/sched/membarrier.c | 1 - > 1 file changed, 1 deletion(-) > > diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c > index eb73eeaedc7d..c38014c2ed66 100644 > --- a/kernel/sched/membarrier.c > +++ b/kernel/sched/membarrier.c > @@ -285,7 +285,6 @@ void membarrier_exec_mmap(struct mm_struct *mm) > * clearing this state. > */ > smp_mb(); > - atomic_set(&mm->membarrier_state, 0); > /* > * Keep the runqueue membarrier_state in sync with this mm > * membarrier_state. > -- > 2.33.1 -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com