Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754754Ab1FFR4P (ORCPT ); Mon, 6 Jun 2011 13:56:15 -0400 Received: from mga02.intel.com ([134.134.136.20]:64500 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751607Ab1FFR4O (ORCPT ); Mon, 6 Jun 2011 13:56:14 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.65,327,1304319600"; d="scan'208";a="9777295" Message-ID: <4DED14BD.9000706@linux.intel.com> Date: Mon, 06 Jun 2011 10:56:13 -0700 From: Darren Hart User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110424 Lightning/1.0b2 Thunderbird/3.1.10 MIME-Version: 1.0 To: Steven Rostedt CC: Eric Dumazet , Peter Zijlstra , David Oliver , linux-kernel@vger.kernel.org, Shawn Bohrer , Zachary Vonler , KOSAKI Motohiro , Hugh Dickins , Thomas Gleixner , Ingo Molnar Subject: Re: Change in functionality of futex() system call. References: <1307373819.3098.40.camel@edumazet-laptop> <1307376672.2322.167.camel@twins> <1307376989.2322.171.camel@twins> <1307377349.3098.65.camel@edumazet-laptop> <1307377782.2322.183.camel@twins> <1307378564.3098.67.camel@edumazet-laptop> <1307379926.2322.219.camel@twins> <1307380297.3098.74.camel@edumazet-laptop> <20110606172707.GB27245@home.goodmis.org> In-Reply-To: <20110606172707.GB27245@home.goodmis.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1767 Lines: 43 On 06/06/2011 10:27 AM, Steven Rostedt wrote: > On Mon, Jun 06, 2011 at 07:11:37PM +0200, Eric Dumazet wrote: >> Le lundi 06 juin 2011 ? 19:05 +0200, Peter Zijlstra a ?crit : >> >>> Dunno, using futexes on private file maps is stupid imo, its just asking >>> for trouble, ro private file maps are even worse. Forcing the COW is the >>> only sane answer in that it gives consistent results and 'breaks' silly >>> expectations early instead of sometimes. >>> >>> Anyway, that's not really the issue here, as David uses MAP_SHARED (as >>> one should if one is interested in the shared value). >> >> Sure, but maybe another guy is 'stupid' and uses MAP_PRIVATE on its >> read-only mappings. With old kernels this was working, and we were not >> doing the COW. > > That sounds like a bug in both the kernel and userspace. I would expect > a MAP_PRIVATE not be seen by any other process regardless. That's the > definition of PRIVATE. > > From: http://www.gnu.org/s/hello/manual/libc/Memory_002dmapped-I_002fO.html > > MAP_PRIVATE > This specifies that writes to the region should never be written back > to the attached file. Instead, a copy is made for the process, and the > region will be swapped normally if memory runs low. No other process > will see the changes. This doesn't address what happens if changes to a MAP_SHARED mapping are visible to a MAP_PRIVATE mapping, which is more the issue at hand I believe. -- Darren Hart Intel Open Source Technology Center Yocto Project - Linux Kernel -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/