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=-0.8 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 C60BDFC6198 for ; Tue, 5 Nov 2019 10:06:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9B3462190F for ; Tue, 5 Nov 2019 10:06:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="inKFBza4" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388201AbfKEKGk (ORCPT ); Tue, 5 Nov 2019 05:06:40 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:51102 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1730711AbfKEKGk (ORCPT ); Tue, 5 Nov 2019 05:06:40 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1572948399; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=cxh+b8Zk81Uj86ZXD24/0mn4MPIM+6Xqq2DkuEn+yZE=; b=inKFBza40ZIJjZwoffaaWYx7tlBvVAqAgTuONuJI4RbTNSua8Cu5vAUjiJyQ8v+QceCddU G5vynCVMz9qOeexWDvqXBKfSqo6bJeUlI72O0xHoAaHeULFPyiiTyTiqGD78si46ihIMd2 5YFRQ4m9BRHbeWFg+GYwgptwPi1UGyQ= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-46-fpr2-B8NOsapmixi-wTVVQ-1; Tue, 05 Nov 2019 05:06:36 -0500 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 13304107ACC2; Tue, 5 Nov 2019 10:06:34 +0000 (UTC) Received: from oldenburg2.str.redhat.com (ovpn-117-86.ams2.redhat.com [10.36.117.86]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BF7F45D713; Tue, 5 Nov 2019 10:06:27 +0000 (UTC) From: Florian Weimer To: Thomas Gleixner Cc: Shawn Landden , libc-alpha@sourceware.org, linux-api@vger.kernel.org, LKML , Arnd Bergmann , Deepa Dinamani , Oleg Nesterov , Andrew Morton , Catalin Marinas , Keith Packard , Peter Zijlstra Subject: Re: [RFC v2 PATCH] futex: extend set_robust_list to allow 2 locking ABIs at the same time. References: <20191104002909.25783-1-shawn@git.icu> <87woceslfs.fsf@oldenburg2.str.redhat.com> Date: Tue, 05 Nov 2019 11:06:25 +0100 In-Reply-To: (Thomas Gleixner's message of "Tue, 5 Nov 2019 10:59:24 +0100 (CET)") Message-ID: <87sgn2skm6.fsf@oldenburg2.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-MC-Unique: fpr2-B8NOsapmixi-wTVVQ-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Thomas Gleixner: > On Tue, 5 Nov 2019, Florian Weimer wrote: >> * Shawn Landden: >> > If this new ABI is used, then bit 1 of the *next pointer of the >> > user-space robust_list indicates that the futex_offset2 value should >> > be used in place of the existing futex_offset. >>=20 >> The futex interface currently has some races which can only be fixed by >> API changes. I'm concerned that we sacrifice the last bit for some >> rather obscure feature. What if we need that bit for fixing the >> correctness issues? > > That current approach is going nowhere and if we change the ABI ever then > this needs to happen with all *libc folks involved and agreeing. > > Out of curiosity, what's the race issue vs. robust list which you are > trying to solve? Sadly I'm not trying to solve them. Here's one of the issues: I think there are others, but I can't find a reference to them. If anyone wants to work on this, I can dig out the details and ask some folks who have looked at this in the past. Thanks, Florian