Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933062AbaGWSZa (ORCPT ); Wed, 23 Jul 2014 14:25:30 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:54462 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932740AbaGWSZ2 (ORCPT ); Wed, 23 Jul 2014 14:25:28 -0400 Date: Wed, 23 Jul 2014 20:25:18 +0200 From: Peter Zijlstra To: Linus Torvalds Cc: Dietmar Eggemann , Michel =?iso-8859-1?Q?D=E4nzer?= , Ingo Molnar , Linux Kernel Mailing List Subject: Re: Random panic in load_balance() with 3.16-rc Message-ID: <20140723182518.GD3935@laptop> References: <53CF844A.5050106@arm.com> <20140723111110.GT3935@laptop> <20140723113021.GP12054@laptop.lan> <20140723142454.GQ12054@laptop.lan> <20140723155526.GW3935@laptop> <20140723170324.GZ3935@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Wed, Jul 23, 2014 at 10:26:21AM -0700, Linus Torvalds wrote: > On Wed, Jul 23, 2014 at 10:12 AM, Linus Torvalds > wrote: > > > > sched_init() definitely does _not_ allocate a cpumask_var. > > Side note: another good rule of thumb for per-cpu variables is: > > - if you use __get_cpu_var() without taking the address of it, you're > doing something wrong and stupid. > > The whole - and really *only* - point of __get_cpu_var is to get the > address of a a cpu variable. If you want to read the *value* of the > variable, you should use "this_cpu_read()", which can use things like > special instructions or segments to read the percpu area. I think this code predates all the this_cpu* magic. But yes, agreed. > I agree that the interface is not all that great, there's historical > baggage there. We would have been better off with > "__this_cpu_ptr(var)" instead of "&__get_cpu_var(var)". But that > "__get_cpu_var()" is the old way of doing things (predating the new > and better "this_cpu_read/write/ops()" stuff), which is why we have > that odd interface with "&__get_cpu_var()". I think there's a whole bunch of patches by Christoph Lameter, queued by TJ that remove all __get_cpu_var usage and eventually the interface. -- 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/