From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B416DC43603 for ; Wed, 4 Dec 2019 14:07:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 841DB206DF for ; Wed, 4 Dec 2019 14:07:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727973AbfLDOHC (ORCPT ); Wed, 4 Dec 2019 09:07:02 -0500 Received: from foss.arm.com ([217.140.110.172]:56326 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727828AbfLDOHC (ORCPT ); Wed, 4 Dec 2019 09:07:02 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 8F2EA1FB; Wed, 4 Dec 2019 06:07:01 -0800 (PST) Received: from [10.1.194.37] (e113632-lin.cambridge.arm.com [10.1.194.37]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 57EBE3F68E; Wed, 4 Dec 2019 06:07:00 -0800 (PST) Subject: Re: Null pointer crash at find_idlest_group on db845c w/ linus/master To: Vincent Guittot Cc: Qais Yousef , John Stultz , Quentin Perret , Peter Zijlstra , Dietmar Eggemann , Juri Lelli , Patrick Bellasi , Ingo Molnar , lkml References: <20191204094216.u7yld5r3zelp22lf@e107158-lin.cambridge.arm.com> <20191204100925.GA15727@linaro.org> <629cca09-dde7-5d77-42e1-c68f2c1820d2@arm.com> From: Valentin Schneider Message-ID: Date: Wed, 4 Dec 2019 14:06:59 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/12/2019 12:08, Vincent Guittot wrote: >> Also; does it really have to involve an affinity "race"? AFAIU affinity >> could have been changed a while back, but the waking CPU isn't allowed >> so we skip the local_group (in simpler cases where each CPU is a group). > > In fact, this will depend of the uninitialized values of local_sgs. I > have been able to reproduce the situation where we skip local group > but not to trigger the crash because the values already in the stack > don't trigger the misfit comparison. > One more thing, DB845 has a single DynamIQ cluster that is represented as a flat hierarchy (unlike regular big.LITTLE, see arch/arm64/boot/dts/qcom/sdm845.dtsi) so we'll just have a single MC level with groups being individual CPUs, making the bug easier to reproduce (than on regular big.LITTLE, that is). > I wait for John feedback to confirm that this fix his problem and > will send a clean version of the patch >> >>