From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758640Ab0DARB6 (ORCPT ); Thu, 1 Apr 2010 13:01:58 -0400 Received: from mx1.redhat.com ([209.132.183.28]:18584 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758254Ab0DARBv (ORCPT ); Thu, 1 Apr 2010 13:01:51 -0400 Date: Thu, 1 Apr 2010 17:36:45 +0200 From: Andrea Arcangeli To: Peter Zijlstra Cc: Avi Kivity , 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() Message-ID: <20100401153645.GP5825@random.random> References: <1270117906.1653.139.camel@laptop> <4BB47FC3.1020606@redhat.com> <1270120592.1653.192.camel@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1270120592.1653.192.camel@laptop> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.