From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754195Ab1I1NDs (ORCPT ); Wed, 28 Sep 2011 09:03:48 -0400 Received: from merlin.infradead.org ([205.233.59.134]:57058 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753504Ab1I1NDr convert rfc822-to-8bit (ORCPT ); Wed, 28 Sep 2011 09:03:47 -0400 Subject: Re: [PATCH] PREEMPT_RT_FULL: arm coredump fails for cpu >= 4 From: Peter Zijlstra To: frank.rowand@am.sony.com Cc: "tglx@linutronix.de" , linux-kernel@vger.kernel.org Date: Wed, 28 Sep 2011 15:03:13 +0200 In-Reply-To: <4E828E35.6070801@am.sony.com> References: <4E828E35.6070801@am.sony.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT X-Mailer: Evolution 3.0.3- Message-ID: <1317214993.24040.16.camel@twins> Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? 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.