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=-11.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 EBDD0C4361B for ; Mon, 14 Dec 2020 18:06:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A53BC224D1 for ; Mon, 14 Dec 2020 18:06:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2408768AbgLNSGe (ORCPT ); Mon, 14 Dec 2020 13:06:34 -0500 Received: from mail.kernel.org ([198.145.29.99]:38164 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2408303AbgLNSGK (ORCPT ); Mon, 14 Dec 2020 13:06:10 -0500 X-Gm-Message-State: AOAM532+Iuh/M+D67djNp4+s99wECyST1lxCtY1IhZw1EaHVI0+/JaQ2 E916sJ+XWppP73o2amjy/gamj4BfbNY7MGZzr/97Lg== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1607969130; bh=rAaVfHwnElycFCW/txpY82sI5mEz7/7D/XkiCH7nAxs=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=U0cd+4uDEePQwse8+8APKunOZ/tDjqSWFYL+2PPRj9Kdu/7qaDci0Z5hTrSAFczzF rKrIWQOTrnXogWqQS5gocuQzmniHnxiTBtlfFwJM5Wkv94wTKimg00ePrtA4lz2aIb TO5h4nrV6Gk6dCuT9oqOvFKqcHHxxfdL5xMpRhX7rhqeYjkwa4cI4l8ndM0nyIJrZ6 mOjrIj+qCL0hOkyuGyxjSj4d3tGeBh6VqU4hOBvidENFwCXeQJq6ORNHu68L8WPLIZ g7r9tt7boM6N+HEasPe2Y73qPoXemNkPbjrgHU/NCRMPPuEP/y+hWgGTZZzv74TaPJ hONUnblH/cGCg== X-Google-Smtp-Source: ABdhPJxfn6S4mVr9Zd7vPIFH7/vXr1SlgoPxayWAiaO86zkxmLkcozP3AR/ZAC/1h72TbkN0IM+oRpphJTrim2gok5o= X-Received: by 2002:a5d:4905:: with SMTP id x5mr14778136wrq.75.1607969128267; Mon, 14 Dec 2020 10:05:28 -0800 (PST) MIME-Version: 1.0 References: <160750336770.3364.7388742360472960633.tip-bot2@tip-bot2> In-Reply-To: <160750336770.3364.7388742360472960633.tip-bot2@tip-bot2> From: Andy Lutomirski Date: Mon, 14 Dec 2020 10:05:18 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [tip: x86/urgent] membarrier: Add an actual barrier before rseq_preempt() To: LKML , Greg KH , Sasha Levin Cc: linux-tip-commits@vger.kernel.org, Andy Lutomirski , Thomas Gleixner , Mathieu Desnoyers , stable , X86 ML Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 9, 2020 at 12:42 AM tip-bot2 for Andy Lutomirski wrote: > > The following commit has been merged into the x86/urgent branch of tip: > > Commit-ID: 2ecedd7569080fd05c1a457e8af2165afecfa29f > Gitweb: https://git.kernel.org/tip/2ecedd7569080fd05c1a457e8af2165afecfa29f > Author: Andy Lutomirski > AuthorDate: Thu, 03 Dec 2020 21:07:04 -08:00 > Committer: Thomas Gleixner > CommitterDate: Wed, 09 Dec 2020 09:37:43 +01:00 > > membarrier: Add an actual barrier before rseq_preempt() > > It seems that most RSEQ membarrier users will expect any stores done before > the membarrier() syscall to be visible to the target task(s). While this > is extremely likely to be true in practice, nothing actually guarantees it > by a strict reading of the x86 manuals. Rather than providing this > guarantee by accident and potentially causing a problem down the road, just > add an explicit barrier. > > Fixes: 70216e18e519 ("membarrier: Provide core serializing command, *_SYNC_CORE") Whoops, this got mangled on its way to tip. This should be: Fixes: 2a36ab717e8f ("rseq/membarrier: Add MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ") and this patch does not need to be backported.