Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754271Ab0HWTIG (ORCPT ); Mon, 23 Aug 2010 15:08:06 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:33538 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753419Ab0HWTIF convert rfc822-to-8bit (ORCPT ); Mon, 23 Aug 2010 15:08:05 -0400 Subject: Re: [RFC] mlock/stack guard interaction fixup From: Peter Zijlstra To: Jeremy Fitzhardinge Cc: Linus Torvalds , Ian Jackson , Greg KH , Ian Campbell , linux-kernel@vger.kernel.org, stable@kernel.org, stable-review@kernel.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk In-Reply-To: <4C72C2E9.3070408@goop.org> References: <1282391770.29609.1223.camel@localhost.localdomain> <1282460275.11348.865.camel@localhost.localdomain> <1282462386.11348.871.camel@localhost.localdomain> <1282470917.11348.891.camel@localhost.localdomain> <20100822172548.GB8957@suse.de> <19570.38608.79434.179797@chiark.greenend.org.uk> <1282580751.2605.1997.camel@laptop> <19570.44367.719276.128881@chiark.greenend.org.uk> <4C72C2E9.3070408@goop.org> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Mon, 23 Aug 2010 21:07:37 +0200 Message-ID: <1282590457.2605.2200.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1576 Lines: 30 On Mon, 2010-08-23 at 11:50 -0700, Jeremy Fitzhardinge wrote: > On 08/23/2010 10:34 AM, Linus Torvalds wrote: > > Quite frankly, I personally believe that people who play games with > > mlock are misguided. The _one_ special case is for protecting keys or > > private data that you do not want to hit the disk in some unencrypted > > mode, and quite frankly, you should strive to handle those way more > > specially than just putting them in some random place ("on the stack" > > or "in some malloc()'ed area"). The sane model for doing that is > > generally to explicitly mmap() and mlock the area, so that you get a > > very controlled access pattern, and never have to worry about things > > like COW etc. > > Is that guaranteed to work (in Linux or in general)? mlock has always > meant "won't generate disk IO to fault in/evicted", but does it prevent > dirty pages from being written out so long as they also remain > resident? Or does it depend on the precise type of page you're > mlocking? For example, what does mlock on a shared writeable mapping mean? mlock() simply avoids major faults, nothing more. I think both page migration and page-out for shared pages where some maps are !mlocked can cause unmaps and thus minor faults. mlock and dirty do not interact, they will still be cleaned/written out as normal. -- 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/