Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753782AbbGNVbQ (ORCPT ); Tue, 14 Jul 2015 17:31:16 -0400 Received: from e39.co.us.ibm.com ([32.97.110.160]:44843 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751708AbbGNVbP (ORCPT ); Tue, 14 Jul 2015 17:31:15 -0400 X-Helo: d03dlp01.boulder.ibm.com X-MailFrom: paulmck@linux.vnet.ibm.com X-RcptTo: linux-kernel@vger.kernel.org Date: Tue, 14 Jul 2015 14:31:03 -0700 From: "Paul E. McKenney" To: Russell King - ARM Linux Cc: Fabio Estevam , "linux-arm-kernel@lists.infradead.org" , Peter Zijlstra , rostedt@goodmis.org, linux-kernel Subject: Re: mx6: suspicious RCU usage Message-ID: <20150714213103.GV3717@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20150714160006.GI3717@linux.vnet.ibm.com> <20150714162600.GJ3717@linux.vnet.ibm.com> <20150714204909.GX7557@n2100.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150714204909.GX7557@n2100.arm.linux.org.uk> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15071421-0033-0000-0000-00000527AE84 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1814 Lines: 48 On Tue, Jul 14, 2015 at 09:49:09PM +0100, Russell King - ARM Linux wrote: > 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. OK, that could explain any number of failures. I will leave this issue in your hands, then. Thanx, Paul -- 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/