Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753579AbbGNUt0 (ORCPT ); Tue, 14 Jul 2015 16:49:26 -0400 Received: from pandora.arm.linux.org.uk ([78.32.30.218]:42357 "EHLO pandora.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753238AbbGNUtZ (ORCPT ); Tue, 14 Jul 2015 16:49:25 -0400 Date: Tue, 14 Jul 2015 21:49:09 +0100 From: Russell King - ARM Linux To: "Paul E. McKenney" Cc: Fabio Estevam , "linux-arm-kernel@lists.infradead.org" , Peter Zijlstra , rostedt@goodmis.org, linux-kernel Subject: Re: mx6: suspicious RCU usage Message-ID: <20150714204909.GX7557@n2100.arm.linux.org.uk> References: <20150714160006.GI3717@linux.vnet.ibm.com> <20150714162600.GJ3717@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150714162600.GJ3717@linux.vnet.ibm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1659 Lines: 44 On Tue, Jul 14, 2015 at 09:26:00AM -0700, Paul E. McKenney wrote: > On Tue, Jul 14, 2015 at 01:06:32PM -0300, Fabio Estevam wrote: > > Hi Paul, > > > > On Tue, Jul 14, 2015 at 1:00 PM, Paul E. McKenney > > wrote: > > > > > Does this patch help? > > > > > > https://lkml.org/lkml/2015/5/12/885 > > > > I am using an ARM 32-bit machine, so I used this one instead: > > https://lkml.org/lkml/2015/5/12/892 > > > > , and it fixes the problem. Thanks! > > > > Feel free to add: > > > > Tested-by: Fabio Estevam > > Glad it helped! > > Russell, did you want me to push this, or would you rather take it? If it's the one I'm thinking of (using the generic code) because it doesn't actually solve the problem we have. It may shut up the RCU warning, but it doesn't solve the underlying problem - one which is caused by the use of atomics (which use the exclusive instructions) vs cache line migration between CPUs vs speculative prefetching... It's possible right now that _dirty_ cache lines can be migrated to the dying CPU, which are then lost on power down - and if we disable the caches on the dying CPU, we then can't use exclusives, so atomics (and all of the other normal kernel synchronisation mechanisms) are out of the question. -- FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up according to speedtest.net. -- 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/