Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753521AbcCLRJL (ORCPT ); Sat, 12 Mar 2016 12:09:11 -0500 Received: from mail-wm0-f66.google.com ([74.125.82.66]:34739 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753265AbcCLRJA (ORCPT ); Sat, 12 Mar 2016 12:09:00 -0500 Date: Sat, 12 Mar 2016 18:08:56 +0100 From: Ingo Molnar To: Rich Felker , Linus Torvalds , Andy Lutomirski , the arch/x86 maintainers , Linux Kernel Mailing List , Borislav Petkov , "musl@lists.openwall.com" , Andrew Morton , Thomas Gleixner , Peter Zijlstra , Szabolcs Nagy Subject: Re: [musl] Re: [RFC PATCH] x86/vdso/32: Add AT_SYSINFO cancellation helpers Message-ID: <20160312170856.GC1108@gmail.com> References: <20160309085631.GA3247@gmail.com> <20160309113449.GZ29662@port70.net> <20160310033446.GL9349@brightrain.aerifal.cx> <20160310111646.GA13102@gmail.com> <20160310164104.GM9349@brightrain.aerifal.cx> <20160310180331.GB15940@gmail.com> <20160310232819.GR9349@brightrain.aerifal.cx> <20160311093347.GA17749@gmail.com> <20160311113914.GD29662@port70.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160311113914.GD29662@port70.net> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 968 Lines: 30 (Argh: Mail-Followup-To spam your mailer sets up is nasty!) * Szabolcs Nagy wrote: > > 4. A calls cancellation point and syscall correctly executes > > 5. Once A enables cancellation again, the cancellation propagates. > > > > So I still see no problem. > > i think the sticky signal design would work, but more > complex than what we have and adds some atomic rmw ops > into common code paths and not backward compatible. Agreed about complexity, but note that the RMW ops shouldn't really be expensive here, as this should be a well-cached flag. Especially compared to: > not using vsyscalls for cancellation-points sounds easier. ... FYI not using vsyscalls has _far_ higher cost than using well-cached RMW ops. So ... what do you think about Linus's SA_SYNCHRONOUS approach? I think it can be made to work without much fuss. There will still be different code paths on old and new kernels, but that's unavoidable. Thanks, Ingo