Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754048AbcDCP6c (ORCPT ); Sun, 3 Apr 2016 11:58:32 -0400 Received: from www.linutronix.de ([62.245.132.108]:59067 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752276AbcDCP6a (ORCPT ); Sun, 3 Apr 2016 11:58:30 -0400 Date: Sun, 3 Apr 2016 17:56:51 +0200 (CEST) From: Thomas Gleixner To: Andy Lutomirski cc: Andy Lutomirski , LKML , Sebastian Andrzej Siewior , Darren Hart , Peter Zijlstra , Ingo Molnar , Michael Kerrisk , Davidlohr Bueso , Chris Mason , "Carlos O'Donell" , Torvald Riegel , Eric Dumazet Subject: Re: [RFC patch 4/7] futex: Add support for attached futexes In-Reply-To: Message-ID: References: <20160402095108.894519835@linutronix.de> <20160402110035.753145539@linutronix.de> <57000D4B.5000406@kernel.org> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1029 Lines: 30 On Sun, 3 Apr 2016, Andy Lutomirski wrote: > On Sun, Apr 3, 2016 at 2:57 AM, Thomas Gleixner wrote: > > On Sat, 2 Apr 2016, Andy Lutomirski wrote: > > > >> On 04/02/2016 04:09 AM, Thomas Gleixner wrote: > >> [omitted due to some Thunderbird bug, sigh] > >> > >> What happens if you mix attached an non-attached ops on the same futex? > > > > Not much. You might get an error code, sleep forever or the call will just > > result in a NOP wasting cpu cycles. That's the same when you mix > > shared/private operations on the same futex. > > What's the workflow? > > Can the creation of an attached futex fail due to memory allocation > problems or any other reason? If so, how does a library make sure it > falls back to a normal futex safely? Well, other operations on futexes can fail as well and the library or the usage site has to take care of it. It's not that different. > Why can't private futexes be attached by default? We _can_ attach any futex - private or not - by default. Thanks, tglx