From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758534Ab0DAQkF (ORCPT ); Thu, 1 Apr 2010 12:40:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:64426 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758436Ab0DAQj5 (ORCPT ); Thu, 1 Apr 2010 12:39:57 -0400 Message-ID: <4BB4BE44.5070507@redhat.com> Date: Thu, 01 Apr 2010 18:39:48 +0300 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.8) Gecko/20100301 Fedora/3.0.3-1.fc12 Thunderbird/3.0.3 MIME-Version: 1.0 To: Andrea Arcangeli CC: Peter Zijlstra , Thomas Gleixner , Rik van Riel , linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Kent Overstreet , Ingo Molnar Subject: Re: [COUNTERPATCH] mm: avoid overflowing preempt_count() in mmu_take_all_locks() References: <1270117906.1653.139.camel@laptop> <4BB47FC3.1020606@redhat.com> <1270120592.1653.192.camel@laptop> <20100401153645.GP5825@random.random> In-Reply-To: <20100401153645.GP5825@random.random> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/01/2010 06:36 PM, Andrea Arcangeli wrote: > On Thu, Apr 01, 2010 at 01:16:32PM +0200, Peter Zijlstra wrote: > >> On Thu, 2010-04-01 at 14:13 +0300, Avi Kivity wrote: >> >> >>> If someone is willing to audit all code paths to make sure these locks >>> are always taken in schedulable context I agree that's a better fix. >>> >> They had better be, they're not irq-safe. Also that's what lockdep is >> for. >> > In my original patchset I included patches from Christoph to convert > those locks to mutexes, there was apparently no problem at all with > that. But frankly I think the only problem here is the warning. The > only compliant we ever had here is from developers, no users at > all. If this was a practical problem I think we should have heard > something by now with so many KVM users out there (and gru too). > > The only single reason I'd go for mutexes would be to accommodate > XPMEM requirements once and for all, no other reason. > There is also a minor benefit for kvm. Reduced latency over large mmu operations; code simplification (we now have some copy_from_user_inatomic() that could be simplified). -- error compiling committee.c: too many arguments to function