From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754973Ab1I1Se1 (ORCPT ); Wed, 28 Sep 2011 14:34:27 -0400 Received: from am1ehsobe002.messaging.microsoft.com ([213.199.154.205]:21187 "EHLO AM1EHSOBE002.bigfish.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753420Ab1I1Se0 (ORCPT ); Wed, 28 Sep 2011 14:34:26 -0400 X-SpamScore: -15 X-BigFish: VPS-15(zzbb2dK936eK1432N98dKzz1202hzzz2fh668h839h93fh61h) X-Spam-TCS-SCL: 0:0 X-Forefront-Antispam-Report: CIP:160.33.98.74;KIP:(null);UIP:(null);IPVD:NLI;H:mail7.fw-bc.sony.com;RD:mail7.fw-bc.sony.com;EFVD:NLI Message-ID: <4E83687D.1070507@am.sony.com> Date: Wed, 28 Sep 2011 11:33:33 -0700 From: Frank Rowand Reply-To: User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110428 Fedora/3.1.10-1.fc14 Thunderbird/3.1.10 MIME-Version: 1.0 To: Peter Zijlstra CC: "Rowand, Frank" , "tglx@linutronix.de" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] PREEMPT_RT_FULL: arm coredump fails for cpu >= 4 References: <4E828E35.6070801@am.sony.com> <1317214993.24040.16.camel@twins> In-Reply-To: <1317214993.24040.16.camel@twins> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-OriginatorOrg: am.sony.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/28/11 06:03, Peter Zijlstra wrote: > On Tue, 2011-09-27 at 20:02 -0700, Frank Rowand wrote: >> >> ARM can not use SPLIT_PTLOCK_CPUS if PREEMPT_RT_FULL because >> vectors_user_mapping() creates a VM_ALWAYSDUMP mapping of the vector page, >> but no ptl->lock has been allocated for the page. An attempt to coredump >> that page will result in a kernel NULL pointer dereference when >> follow_page() attempts to lock the page. > > >> >> This patch is needed only if mm-shrink-the-page-frame-to-rt-size.patch is >> applied. > > Yeah, vile hackery that is.. why isn't pgtable_page_ctor() called on > those pages? Yep, that is the question. I started fixing that yesterday, but realized I was going about it the wrong way, so I sent a first version of the patch that simply avoids the problem. I'll be looking at whether I can fix it cleanly. > > Not that I care too much about split_pte_lock on ARM, they're mostly all > tiny machines anyway so the gain is marginal, but it would be good to > find out why the pgtable constructor isn't called properly. >