From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752869AbbAQAqz (ORCPT ); Fri, 16 Jan 2015 19:46:55 -0500 Received: from mga01.intel.com ([192.55.52.88]:7530 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752309AbbAQAqx (ORCPT ); Fri, 16 Jan 2015 19:46:53 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.97,862,1389772800"; d="scan'208";a="441596010" User-Agent: Microsoft-MacOutlook/14.4.6.141106 Date: Fri, 16 Jan 2015 16:46:39 -0800 Subject: Re: futex(2) man page update help request From: Darren Hart To: "Michael Kerrisk (man-pages)" , Thomas Gleixner CC: "Carlos O'Donell" , Ingo Molnar , Jakub Jelinek , "linux-man@vger.kernel.org" , lkml , Davidlohr Bueso , Arnd Bergmann , Steven Rostedt , Peter Zijlstra , Linux API , Torvald Riegel , Roland McGrath , Darren Hart , Anton Blanchard , Petr Baudis , Eric Dumazet , bill o gallmeister , Jan Kiszka , Daniel Wagner , Rich Felker Message-ID: Thread-Topic: futex(2) man page update help request References: <537346E5.4050407@gmail.com> <5373D0CA.2050204@redhat.com> <54B7D87C.3090901@gmail.com> <54B92B71.2090509@gmail.com> <54B97A72.2050205@gmail.com> In-Reply-To: <54B97A72.2050205@gmail.com> Mime-version: 1.0 Content-type: text/plain; charset="US-ASCII" Content-transfer-encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/16/15, 12:54 PM, "Michael Kerrisk (man-pages)" wrote: >On 01/16/2015 04:20 PM, Thomas Gleixner wrote: >> On Fri, 16 Jan 2015, Michael Kerrisk (man-pages) wrote: >> >>> Hello Thomas, >>> >>> On 01/15/2015 11:23 PM, Thomas Gleixner wrote: >>>> On Thu, 15 Jan 2015, Michael Kerrisk (man-pages) wrote: >>>>>> [EINVAL] uaddr equal uaddr2. Requeue to same futex. >>>>> >>>>> ??? I added this, but does this error not occur only for PI requeues? >>>> >>>> It's equally wrong for normal futexes. And its actually the same code >>>> checking for this for all variants. >>> >>> I don't understand "equally wrong" in your reply, I'm sorry. Do you >>> mean: >>> >>> a) This error text should be there for both normal and PI requeues >> >> It is there for both. The requeue code has that check independent of >> the requeue type (normal/pi). It never makes sense to requeue >> something to itself whether normal or pi futex. We added this for PI, >> because there it is harmful, but we did not special case it. So normal >> futexes get the same treatment. > >Hello Thomas, > >Color me stupid, but I can't see this in futex_requeue(). Where is that >check that is "independent of the requeue type (normal/pi)"? > >When I look through futex_requeue(), all the likely looking sources >of EINVAL are governed by a check on the 'requeue_pi' argument. Right, in the non-PI case, I believe there are valid use cases: move to the back of the FIFO, for example (OK, maybe the only example?). Both tests ensuring uaddr1 != uaddr2 are under the requeue_pi conditional block. The second compares the keys in case they are not FUTEX_PRIVATE (uaddrs would be different, but still the same backing store). Thomas, am I missing a test for this someplace else? -- Darren Hart Intel Open Source Technology Center