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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_MUTT autolearn=ham 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 90C82C04AB6 for ; Fri, 31 May 2019 09:12:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5627026690 for ; Fri, 31 May 2019 09:12:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="QGXqZNaa" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727146AbfEaJMw (ORCPT ); Fri, 31 May 2019 05:12:52 -0400 Received: from merlin.infradead.org ([205.233.59.134]:59030 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726617AbfEaJMw (ORCPT ); Fri, 31 May 2019 05:12:52 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=1zywXp4XVtGKirLjahUxV+mvxxARlKH6na7zNEvRC/c=; b=QGXqZNaaODNHqXNHqcWSnYqrQ CDiLuz1ZjVY7p9nkDYfiEmUFGtdVloKFAfRuJeFFf48bImuHqC/sxp6fkA3TCPKFGHRGymXvcs8Qz le4S9bFaNxRQzDqfMv4mdchODYuFYoP8abeI959yyNJjdiIupeQ0X/KcCfxuk+D942w+U63/aX0g7 gYEFf74sweAS6xpi9qa+rXHlkTXdhA9YUGeXb5m6Mgg8uZ6eyqYiAUpSn06dNPSVQJJZwhsT6RJow F9DXgltFOoZN5Oag5n4ofZjrvEZAipqsQsl66wUbKUHmiHzbQWDuzIirzhuVE1YDsXXEM7DFCA51F P91GS1R+Q==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1hWdah-0003F0-7P; Fri, 31 May 2019 09:12:47 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 00C50201B8CFE; Fri, 31 May 2019 11:12:45 +0200 (CEST) Date: Fri, 31 May 2019 11:12:45 +0200 From: Peter Zijlstra To: Oleg Nesterov Cc: Jann Horn , "Eric W . Biederman" , Andrew Morton , Kees Cook , David Howells , kernel list Subject: Re: [PATCH] ptrace: restore smp_rmb() in __ptrace_may_access() Message-ID: <20190531091245.GN2677@hirez.programming.kicks-ass.net> References: <20190529113157.227380-1-jannh@google.com> <20190529162120.GB27659@redhat.com> <20190530120531.GE22536@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190530120531.GE22536@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 30, 2019 at 02:05:31PM +0200, Oleg Nesterov wrote: > > Anyway, looking at it, I think smp_acquire__after_ctrl_dep() doesn't > > make sense here; > > Well I still _think_ it should work, it provides the LOAD-LOAD ordering > and this is what we need. So it hard relies on being part of a control dependency, note how the comment says that architectures that do not do load speculation can override the smp_rmb() default with barrier() (and we used have an architecture that made use of that, although it's been since removed). IOW, it is an error to use smp_acquire__after_ctrl_dep() without an (immediate) preceding branch.