From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758873AbaGXJz2 (ORCPT ); Thu, 24 Jul 2014 05:55:28 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:50145 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933292AbaGXJzX (ORCPT ); Thu, 24 Jul 2014 05:55:23 -0400 Date: Thu, 24 Jul 2014 11:55:17 +0200 From: Peter Zijlstra To: Michel =?iso-8859-1?Q?D=E4nzer?= Cc: Linus Torvalds , Ingo Molnar , Linux Kernel Mailing List Subject: Re: Random panic in load_balance() with 3.16-rc Message-ID: <20140724095517.GS12054@laptop.lan> References: <53CE00EF.70108@daenzer.net> <53CF31AE.30403@daenzer.net> <20140723064948.GK3935@laptop> <53CF6CC4.6090207@daenzer.net> <20140723082819.GR3935@laptop> <20140723092536.GO12054@laptop.lan> <53CF80EE.5050702@daenzer.net> <53D0B358.5010400@daenzer.net> <20140724075157.GJ3935@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140724075157.GJ3935@laptop> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 24, 2014 at 09:51:57AM +0200, Peter Zijlstra wrote: > > I hope the assembly output I sent earlier helps, I'm afraid bisecting > > this could be painful. > > Yeah, lemme go have a look... So I'm not seeing it, the cpus value is kept at -136(%rbp), so -128(%rbp) comes after and that's struct lb_env env. And -140(%rbp) comes before and that ends up being @idle. The compiler likes to spill for sure, but aside from stupid I don't see it doing wrong in the relatively short code from function start to the rep movsl. It does a rep stosl on -128(%rbp) and then fills it out, but none of that looks to stomp on our -136(%rbp) value. And the -140(%rbp) thing is only written to once, and while that is done after the 136 thing its a single movl and that's not going to clobber anything. And the fault happens before we pass @env around, so there no chance someone writes before it either. So I'm still entirely clueless..