Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753357AbcLLVQa (ORCPT ); Mon, 12 Dec 2016 16:16:30 -0500 Received: from mx1.redhat.com ([209.132.183.28]:59964 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752947AbcLLVQ3 (ORCPT ); Mon, 12 Dec 2016 16:16:29 -0500 Date: Mon, 12 Dec 2016 15:16:27 -0600 From: Josh Poimboeuf To: Borislav Petkov Cc: x86-ml , lkml , Andy Lutomirski Subject: Re: WARNING: kernel stack frame pointer at ffffffff82e03f40 in swapper:0 has bad value (null) Message-ID: <20161212211627.yuodrw35xwq3hmn7@treble> References: <20161210161749.gvboowyhtffvpoo3@pd.tnic> <20161210170444.trpnnq4gtkx5djqm@treble> <20161210172802.gpgjjndo56d43mi4@pd.tnic> <20161212154542.ul6cnzjtkbvooluh@treble> <20161212175023.455mlwhmnqfew2nu@pd.tnic> <20161212181025.uz3gk3jasuskqfmf@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20161212181025.uz3gk3jasuskqfmf@treble> User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Mon, 12 Dec 2016 21:16:28 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1313 Lines: 27 On Mon, Dec 12, 2016 at 12:10:25PM -0600, Josh Poimboeuf wrote: > On Mon, Dec 12, 2016 at 06:50:23PM +0100, Borislav Petkov wrote: > > [ 0.000000] ffffffffbce03f40: 0000000000000000 ... > > [ 0.000000] ffffffffbce03f48: ffffffffbc0001b5 (start_cpu+0x5/0x14) > > [ 0.000000] ffffffffbce03f50: ffffffffbc0001b5 (start_cpu+0x5/0x14) > > [ 0.000000] ffffffffbce03f58: 0000000000000000 ... > > [ 0.000000] Linux version 4.9.0-rc8+ (root@gondor) (gcc version 6.2.0 20161109 (Debian 6.2.0-13) ) #2 SMP PREEMPT Mon Dec 12 18:36:48 CET 2016 > > Something funky is going on in the head code. It looks like start_cpu > is getting executed twice somehow. Need to do some more head > scratching... I still can't figure out what could cause this, nor can I recreate it. Andy, any idea? I'm trying to figure out why a stack trace of the initial task, early in start_kernel(), would show start_cpu() on the stack *twice*. The start_cpu() entry on the stack at ffffffffbce03f50 is right where it's supposed to be. But then there's another start_cpu() entry at 0xffffffffbce03f48 which is pointed to by the frame pointer chain. I can't figure out where that one came from and why the stack is offset by a word, compared to all the other idle task stacks I've seen. Boris, what kind of CPU is it? -- Josh