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_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 71FEBC43381 for ; Tue, 26 Feb 2019 10:46:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 32B1B2173C for ; Tue, 26 Feb 2019 10:46:17 +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="oWt1VcQt" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727633AbfBZKqP (ORCPT ); Tue, 26 Feb 2019 05:46:15 -0500 Received: from merlin.infradead.org ([205.233.59.134]:50008 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725954AbfBZKqP (ORCPT ); Tue, 26 Feb 2019 05:46:15 -0500 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=aLtDm31IFnhB2t121sovdtLqgXBuVk+B8akRv5BTmCc=; b=oWt1VcQtHFdljFP0FRbOrpKwp 6zAWOYHJVKwa/rf5AxrKrwbv76+zDtMag9krqky20oqEHwKTJEE+tSZxPDfo9AYcMLpP45k+rOZa5 twTLBvHGgLPuKo6RGojMXDqRyO4NFRxCcDmcRSvHN6xQlaI5oaBuSB7P1KXrjsDgmLuls4DYSXrEw Azo6XDbtaMX3U3jEswHBJeCvuK5mSlsUec9ZY2SD8yEwLjJcsHiSzRJE1xyj+X1fTRPftzR/WNlvu IXS76BmCE6TW5edd5oVR30Ywjkz9aZgWZJjjaMaPHI/2U2mqVyp9w7b/9zpUGkhSqX7ExlJCN23+x imFt6UkUQ==; 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 1gyaFG-0004zv-Gj; Tue, 26 Feb 2019 10:45:54 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id BA4EB20269AFC; Tue, 26 Feb 2019 11:45:51 +0100 (CET) Date: Tue, 26 Feb 2019 11:45:51 +0100 From: Peter Zijlstra To: "Paul E. McKenney" Cc: Andrea Parri , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Alan Stern , Will Deacon , Boqun Feng , Nicholas Piggin , David Howells , Jade Alglave , Luc Maranget , Akira Yokosawa , Daniel Lustig Subject: Re: [RFC PATCH] tools/memory-model: Remove (dep ; rfi) from ppo Message-ID: <20190226104551.GF32534@hirez.programming.kicks-ass.net> References: <1550617057-4911-1-git-send-email-andrea.parri@amarulasolutions.com> <20190220020117.GD11787@linux.ibm.com> <20190220092604.GD32494@hirez.programming.kicks-ass.net> <20190220131456.GA3215@andrea> <20190220132714.GI32494@hirez.programming.kicks-ass.net> <20190222112128.GA7213@andrea> <20190222130014.GY32494@hirez.programming.kicks-ass.net> <20190225175517.GK4072@linux.ibm.com> <20190226093009.GS32477@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190226093009.GS32477@hirez.programming.kicks-ass.net> 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 Tue, Feb 26, 2019 at 10:30:09AM +0100, Peter Zijlstra wrote: > On Mon, Feb 25, 2019 at 09:55:17AM -0800, Paul E. McKenney wrote: > > But if you know of any code in the Linux kernel that needs to compare > > pointers, one of which might be in the process of being freed, please > > do point me at it. > > I'm having the utmost difficulty of understanding why that would be a > problem. It's just a value. Freeing memory does not affect the actual > memory or any pointers to it. > > *confusion* > > None of this makes any kind of sense. I found and started to read: www.open-std.org/jtc1/sc22/wg14/www/docs/n2311.pdf and that's all massive bong-hits. That's utterly insane. Even the proposed semantics are crazy; they include UB and are therefore broken on principle. But also; the provenance ID has words like: "allocated storage duration", how is that well defined in the context of concurrent execution? Also, isn't the kernel filled with inter-object pointer arithmetic? PNVI also looks like something that simply cannot work; how are we at compile time supposed to know the active (concurrent modified) heap layout. What is a 'live' object?